Remove std::string alias (for real this time)

Also use std::string_view in a few more places.

perl/lib/Nix/Store.xs

@@ -240,7 +240,7 @@ SV * convertHash(char * algo, char * s, int toBase32)
     PPCODE:
         try {
             auto h = Hash::parseAny(s, parseHashType(algo));
-            string s = h.to_string(toBase32 ? Base32 : Base16, false);
+            auto s = h.to_string(toBase32 ? Base32 : Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());

src/build-remote/build-remote.cc

@@ -32,7 +32,7 @@ std::string escapeUri(std::string uri)
     return uri;
 }
 
-static string currentLoad;
+static std::string currentLoad;
 
 static AutoCloseFD openSlotLock(const Machine & m, uint64_t slot)
 {
@@ -97,7 +97,7 @@ static int main_build_remote(int argc, char * * argv)
         }
 
         std::optional<StorePath> drvPath;
-        string storeUri;
+        std::string storeUri;
 
         while (true) {
 
@@ -183,7 +183,7 @@ static int main_build_remote(int argc, char * * argv)
                     else
                     {
                         // build the hint template.
-                        string errorText =
+                        std::string errorText =
                             "Failed to find a machine for remote build!\n"
                             "derivation: %s\nrequired (system, features): (%s, %s)";
                         errorText += "\n%s available machines:";
@@ -193,7 +193,7 @@ static int main_build_remote(int argc, char * * argv)
                             errorText += "\n(%s, %s, %s, %s)";
 
                         // add the template values.
-                        string drvstr;
+                        std::string drvstr;
                         if (drvPath.has_value())
                             drvstr = drvPath->to_string();
                         else
@@ -208,7 +208,7 @@ static int main_build_remote(int argc, char * * argv)
 
                         for (auto & m : machines)
                             error
-                                % concatStringsSep<std::vector<string>>(", ", m.systemTypes)
+                                % concatStringsSep<std::vector<std::string>>(", ", m.systemTypes)
                                 % m.maxJobs
                                 % concatStringsSep<StringSet>(", ", m.supportedFeatures)
                                 % concatStringsSep<StringSet>(", ", m.mandatoryFeatures);

src/libexpr/attr-path.cc

@@ -9,7 +9,7 @@ namespace nix {
 static Strings parseAttrPath(std::string_view s)
 {
     Strings res;
-    string cur;
+    std::string cur;
     auto i = s.begin();
     while (i != s.end()) {
         if (*i == '.') {
@@ -41,7 +41,7 @@ std::vector<Symbol> parseAttrPath(EvalState & state, std::string_view s)
 }
 
 
-std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const string & attrPath,
+std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const std::string & attrPath,
     Bindings & autoArgs, Value & vIn)
 {
     Strings tokens = parseAttrPath(attrPath);
@@ -121,7 +121,7 @@ Pos findPackageFilename(EvalState & state, Value & v, std::string what)
     std::string filename(pos, 0, colon);
     unsigned int lineno;
     try {
-        lineno = std::stoi(std::string(pos, colon + 1, string::npos));
+        lineno = std::stoi(std::string(pos, colon + 1, std::string::npos));
     } catch (std::invalid_argument & e) {
         throw ParseError("cannot parse line number '%s'", pos);
     }

src/libexpr/attr-path.hh

@@ -10,8 +10,11 @@ namespace nix {
 MakeError(AttrPathNotFound, Error);
 MakeError(NoPositionInfo, Error);
 
-std::pair<Value *, Pos> findAlongAttrPath(EvalState & state, const string & attrPath,
+std::pair<Value *, Pos> findAlongAttrPath(
-    Bindings & autoArgs, Value & vIn);
+    EvalState & state,
+    const std::string & attrPath,
+    Bindings & autoArgs,
+    Value & vIn);
 
 /* Heuristic to find the filename and lineno or a nix value. */
 Pos findPackageFilename(EvalState & state, Value & v, std::string what);

src/libexpr/attr-set.hh

@@ -105,7 +105,7 @@ public:
         for (size_t n = 0; n < size_; n++)
             res.emplace_back(&attrs[n]);
         std::sort(res.begin(), res.end(), [](const Attr * a, const Attr * b) {
-            return (const string &) a->name < (const string &) b->name;
+            return (const std::string &) a->name < (const std::string &) b->name;
         });
         return res;
     }

src/libexpr/common-eval-args.cc

@@ -77,7 +77,7 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
     for (auto & i : autoArgs) {
         auto v = state.allocValue();
         if (i.second[0] == 'E')
-            state.mkThunk_(*v, state.parseExprFromString(string(i.second, 1), absPath(".")));
+            state.mkThunk_(*v, state.parseExprFromString(i.second.substr(1), absPath(".")));
         else
             v->mkString(((std::string_view) i.second).substr(1));
         res.insert(state.symbols.create(i.first), v);
@@ -85,17 +85,17 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
     return res.finish();
 }
 
-Path lookupFileArg(EvalState & state, string s)
+Path lookupFileArg(EvalState & state, std::string_view s)
 {
     if (isUri(s)) {
         return state.store->toRealPath(
             fetchers::downloadTarball(
                 state.store, resolveUri(s), "source", false).first.storePath);
     } else if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
-        Path p = s.substr(1, s.size() - 2);
+        Path p(s.substr(1, s.size() - 2));
         return state.findFile(p);
     } else
-        return absPath(s);
+        return absPath(std::string(s));
 }
 
 }

src/libexpr/common-eval-args.hh

@@ -22,6 +22,6 @@ private:
     std::map<std::string, std::string> autoArgs;
 };
 
-Path lookupFileArg(EvalState & state, string s);
+Path lookupFileArg(EvalState & state, std::string_view s);
 
 }

src/libexpr/eval-cache.cc

@@ -596,7 +596,7 @@ std::vector<Symbol> AttrCursor::getAttrs()
     for (auto & attr : *getValue().attrs)
         attrs.push_back(attr.name);
     std::sort(attrs.begin(), attrs.end(), [](const Symbol & a, const Symbol & b) {
-        return (const string &) a < (const string &) b;
+        return (const std::string &) a < (const std::string &) b;
     });
 
     if (root->db)

src/libexpr/eval.cc

@@ -183,7 +183,7 @@ const Value *getPrimOp(const Value &v) {
     return primOp;
 }
 
-string showType(ValueType type)
+std::string_view showType(ValueType type)
 {
     switch (type) {
         case nInt: return "an integer";
@@ -202,20 +202,20 @@ string showType(ValueType type)
 }
 
 
-string showType(const Value & v)
+std::string showType(const Value & v)
 {
     switch (v.internalType) {
         case tString: return v.string.context ? "a string with context" : "a string";
         case tPrimOp:
-            return fmt("the built-in function '%s'", string(v.primOp->name));
+            return fmt("the built-in function '%s'", std::string(v.primOp->name));
         case tPrimOpApp:
-            return fmt("the partially applied built-in function '%s'", string(getPrimOp(v)->primOp->name));
+            return fmt("the partially applied built-in function '%s'", std::string(getPrimOp(v)->primOp->name));
         case tExternal: return v.external->showType();
         case tThunk: return "a thunk";
         case tApp: return "a function application";
         case tBlackhole: return "a black hole";
     default:
-        return showType(v.type());
+        return std::string(showType(v.type()));
     }
 }
 
@@ -356,7 +356,7 @@ void initGC()
 
 /* Very hacky way to parse $NIX_PATH, which is colon-separated, but
    can contain URLs (e.g. "nixpkgs=https://bla...:foo=https://"). */
-static Strings parseNixPath(const string & s)
+static Strings parseNixPath(const std::string & s)
 {
     Strings res;
 
@@ -606,7 +606,7 @@ Path EvalState::toRealPath(const Path & path, const PathSet & context)
 }
 
 
-Value * EvalState::addConstant(const string & name, Value & v)
+Value * EvalState::addConstant(const std::string & name, Value & v)
 {
     Value * v2 = allocValue();
     *v2 = v;
@@ -615,19 +615,19 @@ Value * EvalState::addConstant(const string & name, Value & v)
 }
 
 
-void EvalState::addConstant(const string & name, Value * v)
+void EvalState::addConstant(const std::string & name, Value * v)
 {
     staticBaseEnv.vars.emplace_back(symbols.create(name), baseEnvDispl);
     baseEnv.values[baseEnvDispl++] = v;
-    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    auto name2 = name.substr(0, 2) == "__" ? name.substr(2) : name;
     baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v));
 }
 
 
-Value * EvalState::addPrimOp(const string & name,
+Value * EvalState::addPrimOp(const std::string & name,
     size_t arity, PrimOpFun primOp)
 {
-    auto name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    auto name2 = name.substr(0, 2) == "__" ? name.substr(2) : name;
     Symbol sym = symbols.create(name2);
 
     /* Hack to make constants lazy: turn them into a application of
@@ -675,7 +675,7 @@ Value * EvalState::addPrimOp(PrimOp && primOp)
 }
 
 
-Value & EvalState::getBuiltin(const string & name)
+Value & EvalState::getBuiltin(const std::string & name)
 {
     return *baseEnv.values[0]->attrs->find(symbols.create(name))->value;
 }
@@ -703,12 +703,12 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
    evaluator.  So here are some helper functions for throwing
    exceptions. */
 
-LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2))
+LocalNoInlineNoReturn(void throwEvalError(const char * s, const std::string & s2))
 {
     throw EvalError(s, s2);
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const string & s2))
+LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const std::string & s2))
 {
     throw EvalError({
         .msg = hintfmt(s, s2),
@@ -716,12 +716,12 @@ LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const
     });
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2, const string & s3))
+LocalNoInlineNoReturn(void throwEvalError(const char * s, const std::string & s2, const std::string & s3))
 {
     throw EvalError(s, s2, s3);
 }
 
-LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const string & s2, const string & s3))
+LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const std::string & s2, const std::string & s3))
 {
     throw EvalError({
         .msg = hintfmt(s, s2, s3),
@@ -759,7 +759,7 @@ LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v))
     throw TypeError(s, showType(v));
 }
 
-LocalNoInlineNoReturn(void throwAssertionError(const Pos & pos, const char * s, const string & s1))
+LocalNoInlineNoReturn(void throwAssertionError(const Pos & pos, const char * s, const std::string & s1))
 {
     throw AssertionError({
         .msg = hintfmt(s, s1),
@@ -767,7 +767,7 @@ LocalNoInlineNoReturn(void throwAssertionError(const Pos & pos, const char * s,
     });
 }
 
-LocalNoInlineNoReturn(void throwUndefinedVarError(const Pos & pos, const char * s, const string & s1))
+LocalNoInlineNoReturn(void throwUndefinedVarError(const Pos & pos, const char * s, const std::string & s1))
 {
     throw UndefinedVarError({
         .msg = hintfmt(s, s1),
@@ -775,7 +775,7 @@ LocalNoInlineNoReturn(void throwUndefinedVarError(const Pos & pos, const char *
     });
 }
 
-LocalNoInlineNoReturn(void throwMissingArgumentError(const Pos & pos, const char * s, const string & s1))
+LocalNoInlineNoReturn(void throwMissingArgumentError(const Pos & pos, const char * s, const std::string & s1))
 {
     throw MissingArgumentError({
         .msg = hintfmt(s, s1),
@@ -783,12 +783,12 @@ LocalNoInlineNoReturn(void throwMissingArgumentError(const Pos & pos, const char
     });
 }
 
-LocalNoInline(void addErrorTrace(Error & e, const char * s, const string & s2))
+LocalNoInline(void addErrorTrace(Error & e, const char * s, const std::string & s2))
 {
     e.addTrace(std::nullopt, s, s2);
 }
 
-LocalNoInline(void addErrorTrace(Error & e, const Pos & pos, const char * s, const string & s2))
+LocalNoInline(void addErrorTrace(Error & e, const Pos & pos, const char * s, const std::string & s2))
 {
     e.addTrace(pos, s, s2);
 }
@@ -1221,7 +1221,7 @@ void ExprVar::eval(EvalState & state, Env & env, Value & v)
 }
 
 
-static string showAttrPath(EvalState & state, Env & env, const AttrPath & attrPath)
+static std::string showAttrPath(EvalState & state, Env & env, const AttrPath & attrPath)
 {
     std::ostringstream out;
     bool first = true;
@@ -1395,7 +1395,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 if (loggerSettings.showTrace.get()) {
                     addErrorTrace(e, lambda.pos, "while evaluating %s",
                         (lambda.name.set()
-                            ? "'" + (string) lambda.name + "'"
+                            ? "'" + (const std::string &) lambda.name + "'"
                             : "anonymous lambda"));
                     addErrorTrace(e, pos, "from call site%s", "");
                 }
@@ -1883,7 +1883,7 @@ std::string_view EvalState::forceString(Value & v, const Pos & pos)
 
 /* Decode a context string ‘!<name>!<path>’ into a pair <path,
    name>. */
-std::pair<string, string> decodeContext(std::string_view s)
+std::pair<std::string, std::string> decodeContext(std::string_view s)
 {
     if (s.at(0) == '!') {
         size_t index = s.find("!", 1);
@@ -1946,7 +1946,7 @@ bool EvalState::isDerivation(Value & v)
 }
 
 
-std::optional<string> EvalState::tryAttrsToString(const Pos & pos, Value & v,
+std::optional<std::string> EvalState::tryAttrsToString(const Pos & pos, Value & v,
     PathSet & context, bool coerceMore, bool copyToStore)
 {
     auto i = v.attrs->find(sToString);
@@ -2001,7 +2001,7 @@ BackedStringView EvalState::coerceToString(const Pos & pos, Value & v, PathSet &
         if (v.type() == nNull) return "";
 
         if (v.isList()) {
-            string result;
+            std::string result;
             for (auto [n, v2] : enumerate(v.listItems())) {
                 result += *coerceToString(pos, *v2, context, coerceMore, copyToStore);
                 if (n < v.listSize() - 1
@@ -2017,7 +2017,7 @@ BackedStringView EvalState::coerceToString(const Pos & pos, Value & v, PathSet &
 }
 
 
-string EvalState::copyPathToStore(PathSet & context, const Path & path)
+std::string EvalState::copyPathToStore(PathSet & context, const Path & path)
 {
     if (nix::isDerivation(path))
         throwEvalError("file names are not allowed to end in '%1%'", drvExtension);
@@ -2043,7 +2043,7 @@ string EvalState::copyPathToStore(PathSet & context, const Path & path)
 
 Path EvalState::coerceToPath(const Pos & pos, Value & v, PathSet & context)
 {
-    string path = coerceToString(pos, v, context, false, false).toOwned();
+    auto path = coerceToString(pos, v, context, false, false).toOwned();
     if (path == "" || path[0] != '/')
         throwEvalError(pos, "string '%1%' doesn't represent an absolute path", path);
     return path;
@@ -2213,11 +2213,11 @@ void EvalState::printStats()
                 for (auto & i : functionCalls) {
                     auto obj = list.object();
                     if (i.first->name.set())
-                        obj.attr("name", (const string &) i.first->name);
+                        obj.attr("name", (const std::string &) i.first->name);
                     else
                         obj.attr("name", nullptr);
                     if (i.first->pos) {
-                        obj.attr("file", (const string &) i.first->pos.file);
+                        obj.attr("file", (const std::string &) i.first->pos.file);
                         obj.attr("line", i.first->pos.line);
                         obj.attr("column", i.first->pos.column);
                     }
@@ -2229,7 +2229,7 @@ void EvalState::printStats()
                 for (auto & i : attrSelects) {
                     auto obj = list.object();
                     if (i.first) {
-                        obj.attr("file", (const string &) i.first.file);
+                        obj.attr("file", (const std::string &) i.first.file);
                         obj.attr("line", i.first.line);
                         obj.attr("column", i.first.column);
                     }
@@ -2246,7 +2246,7 @@ void EvalState::printStats()
 }
 
 
-string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const
+std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const
 {
     throw TypeError({
         .msg = hintfmt("cannot coerce %1% to a string", showType()),

src/libexpr/eval.hh

@@ -150,7 +150,7 @@ public:
         const Pos & pos
     );
 
-    void addToSearchPath(const string & s);
+    void addToSearchPath(const std::string & s);
 
     SearchPath getSearchPath() { return searchPath; }
 
@@ -251,7 +251,7 @@ public:
        set with attribute `type = "derivation"'). */
     bool isDerivation(Value & v);
 
-    std::optional<string> tryAttrsToString(const Pos & pos, Value & v,
+    std::optional<std::string> tryAttrsToString(const Pos & pos, Value & v,
         PathSet & context, bool coerceMore = false, bool copyToStore = true);
 
     /* String coercion.  Converts strings, paths and derivations to a
@@ -262,7 +262,7 @@ public:
         bool coerceMore = false, bool copyToStore = true,
         bool canonicalizePath = true);
 
-    string copyPathToStore(PathSet & context, const Path & path);
+    std::string copyPathToStore(PathSet & context, const Path & path);
 
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
@@ -284,18 +284,18 @@ private:
 
     void createBaseEnv();
 
-    Value * addConstant(const string & name, Value & v);
+    Value * addConstant(const std::string & name, Value & v);
 
-    void addConstant(const string & name, Value * v);
+    void addConstant(const std::string & name, Value * v);
 
-    Value * addPrimOp(const string & name,
+    Value * addPrimOp(const std::string & name,
         size_t arity, PrimOpFun primOp);
 
     Value * addPrimOp(PrimOp && primOp);
 
 public:
 
-    Value & getBuiltin(const string & name);
+    Value & getBuiltin(const std::string & name);
 
     struct Doc
     {
@@ -414,12 +414,12 @@ private:
 
 
 /* Return a string representing the type of the value `v'. */
-string showType(ValueType type);
+std::string_view showType(ValueType type);
-string showType(const Value & v);
+std::string showType(const Value & v);
 
 /* Decode a context string ‘!<name>!<path>’ into a pair <path,
    name>. */
-std::pair<string, string> decodeContext(std::string_view s);
+std::pair<std::string, std::string> decodeContext(std::string_view s);
 
 /* If `path' refers to a directory, then append "/default.nix". */
 Path resolveExprPath(Path path);

src/libexpr/flake/flake.cc

@@ -254,7 +254,7 @@ static Flake getFlake(
         for (auto & setting : *nixConfig->value->attrs) {
             forceTrivialValue(state, *setting.value, *setting.pos);
             if (setting.value->type() == nString)
-                flake.config.settings.insert({setting.name, string(state.forceStringNoCtx(*setting.value, *setting.pos))});
+                flake.config.settings.insert({setting.name, std::string(state.forceStringNoCtx(*setting.value, *setting.pos))});
             else if (setting.value->type() == nPath) {
                 PathSet emptyContext = {};
                 flake.config.settings.emplace(
@@ -707,7 +707,7 @@ static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Va
 {
     state.requireExperimentalFeatureOnEvaluation(Xp::Flakes, "builtins.getFlake", pos);
 
-    string flakeRefS(state.forceStringNoCtx(*args[0], pos));
+    std::string flakeRefS(state.forceStringNoCtx(*args[0], pos));
     auto flakeRef = parseFlakeRef(flakeRefS, {}, true);
     if (evalSettings.pureEval && !flakeRef.input.isLocked())
         throw Error("cannot call 'getFlake' on unlocked flake reference '%s', at %s (use --impure to override)", flakeRefS, pos);

src/libexpr/get-drvs.cc

@@ -11,8 +11,8 @@
 namespace nix {
 
 
-DrvInfo::DrvInfo(EvalState & state, const string & attrPath, Bindings * attrs)
+DrvInfo::DrvInfo(EvalState & state, std::string attrPath, Bindings * attrs)
-    : state(&state), attrs(attrs), attrPath(attrPath)
+    : state(&state), attrs(attrs), attrPath(std::move(attrPath))
 {
 }
 
@@ -47,7 +47,7 @@ DrvInfo::DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPat
 }
 
 
-string DrvInfo::queryName() const
+std::string DrvInfo::queryName() const
 {
     if (name == "" && attrs) {
         auto i = attrs->find(state->sName);
@@ -58,7 +58,7 @@ string DrvInfo::queryName() const
 }
 
 
-string DrvInfo::querySystem() const
+std::string DrvInfo::querySystem() const
 {
     if (system == "" && attrs) {
         auto i = attrs->find(state->sSystem);
@@ -68,7 +68,7 @@ string DrvInfo::querySystem() const
 }
 
 
-string DrvInfo::queryDrvPath() const
+std::string DrvInfo::queryDrvPath() const
 {
     if (drvPath == "" && attrs) {
         Bindings::iterator i = attrs->find(state->sDrvPath);
@@ -79,7 +79,7 @@ string DrvInfo::queryDrvPath() const
 }
 
 
-string DrvInfo::queryOutPath() const
+std::string DrvInfo::queryOutPath() const
 {
     if (!outPath && attrs) {
         Bindings::iterator i = attrs->find(state->sOutPath);
@@ -104,7 +104,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool onlyOutputsToInstall)
             /* For each output... */
             for (auto elem : i->value->listItems()) {
                 /* Evaluate the corresponding set. */
-                string name(state->forceStringNoCtx(*elem, *i->pos));
+                std::string name(state->forceStringNoCtx(*elem, *i->pos));
                 Bindings::iterator out = attrs->find(state->symbols.create(name));
                 if (out == attrs->end()) continue; // FIXME: throw error?
                 state->forceAttrs(*out->value, *i->pos);
@@ -138,7 +138,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool onlyOutputsToInstall)
 }
 
 
-string DrvInfo::queryOutputName() const
+std::string DrvInfo::queryOutputName() const
 {
     if (outputName == "" && attrs) {
         Bindings::iterator i = attrs->find(state->sOutputName);
@@ -190,7 +190,7 @@ bool DrvInfo::checkMeta(Value & v)
 }
 
 
-Value * DrvInfo::queryMeta(const string & name)
+Value * DrvInfo::queryMeta(const std::string & name)
 {
     if (!getMeta()) return 0;
     Bindings::iterator a = meta->find(state->symbols.create(name));
@@ -199,7 +199,7 @@ Value * DrvInfo::queryMeta(const string & name)
 }
 
 
-string DrvInfo::queryMetaString(const string & name)
+std::string DrvInfo::queryMetaString(const std::string & name)
 {
     Value * v = queryMeta(name);
     if (!v || v->type() != nString) return "";
@@ -207,7 +207,7 @@ string DrvInfo::queryMetaString(const string & name)
 }
 
 
-NixInt DrvInfo::queryMetaInt(const string & name, NixInt def)
+NixInt DrvInfo::queryMetaInt(const std::string & name, NixInt def)
 {
     Value * v = queryMeta(name);
     if (!v) return def;
@@ -221,7 +221,7 @@ NixInt DrvInfo::queryMetaInt(const string & name, NixInt def)
     return def;
 }
 
-NixFloat DrvInfo::queryMetaFloat(const string & name, NixFloat def)
+NixFloat DrvInfo::queryMetaFloat(const std::string & name, NixFloat def)
 {
     Value * v = queryMeta(name);
     if (!v) return def;
@@ -236,7 +236,7 @@ NixFloat DrvInfo::queryMetaFloat(const string & name, NixFloat def)
 }
 
 
-bool DrvInfo::queryMetaBool(const string & name, bool def)
+bool DrvInfo::queryMetaBool(const std::string & name, bool def)
 {
     Value * v = queryMeta(name);
     if (!v) return def;
@@ -251,7 +251,7 @@ bool DrvInfo::queryMetaBool(const string & name, bool def)
 }
 
 
-void DrvInfo::setMeta(const string & name, Value * v)
+void DrvInfo::setMeta(const std::string & name, Value * v)
 {
     getMeta();
     auto attrs = state->buildBindings(1 + (meta ? meta->size() : 0));
@@ -274,7 +274,7 @@ typedef std::set<Bindings *> Done;
    The result boolean indicates whether it makes sense
    for the caller to recursively search for derivations in `v'. */
 static bool getDerivation(EvalState & state, Value & v,
-    const string & attrPath, DrvInfos & drvs, Done & done,
+    const std::string & attrPath, DrvInfos & drvs, Done & done,
     bool ignoreAssertionFailures)
 {
     try {
@@ -311,7 +311,7 @@ std::optional<DrvInfo> getDerivation(EvalState & state, Value & v,
 }
 
 
-static string addToPath(const string & s1, const string & s2)
+static std::string addToPath(const std::string & s1, const std::string & s2)
 {
     return s1.empty() ? s2 : s1 + "." + s2;
 }
@@ -321,7 +321,7 @@ static std::regex attrRegex("[A-Za-z_][A-Za-z0-9-_+]*");
 
 
 static void getDerivations(EvalState & state, Value & vIn,
-    const string & pathPrefix, Bindings & autoArgs,
+    const std::string & pathPrefix, Bindings & autoArgs,
     DrvInfos & drvs, Done & done,
     bool ignoreAssertionFailures)
 {
@@ -346,7 +346,7 @@ static void getDerivations(EvalState & state, Value & vIn,
             debug("evaluating attribute '%1%'", i->name);
             if (!std::regex_match(std::string(i->name), attrRegex))
                 continue;
-            string pathPrefix2 = addToPath(pathPrefix, i->name);
+            std::string pathPrefix2 = addToPath(pathPrefix, i->name);
             if (combineChannels)
                 getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
             else if (getDerivation(state, *i->value, pathPrefix2, drvs, done, ignoreAssertionFailures)) {
@@ -364,7 +364,7 @@ static void getDerivations(EvalState & state, Value & vIn,
 
     else if (v.type() == nList) {
         for (auto [n, elem] : enumerate(v.listItems())) {
-            string pathPrefix2 = addToPath(pathPrefix, fmt("%d", n));
+            std::string pathPrefix2 = addToPath(pathPrefix, fmt("%d", n));
             if (getDerivation(state, *elem, pathPrefix2, drvs, done, ignoreAssertionFailures))
                 getDerivations(state, *elem, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
         }
@@ -374,7 +374,7 @@ static void getDerivations(EvalState & state, Value & vIn,
 }
 
 
-void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
+void getDerivations(EvalState & state, Value & v, const std::string & pathPrefix,
     Bindings & autoArgs, DrvInfos & drvs, bool ignoreAssertionFailures)
 {
     Done done;

src/libexpr/get-drvs.hh

@@ -12,16 +12,16 @@ namespace nix {
 struct DrvInfo
 {
 public:
-    typedef std::map<string, Path> Outputs;
+    typedef std::map<std::string, Path> Outputs;
 
 private:
     EvalState * state;
 
-    mutable string name;
+    mutable std::string name;
-    mutable string system;
+    mutable std::string system;
-    mutable string drvPath;
+    mutable std::string drvPath;
-    mutable std::optional<string> outPath;
+    mutable std::optional<std::string> outPath;
-    mutable string outputName;
+    mutable std::string outputName;
     Outputs outputs;
 
     bool failed = false; // set if we get an AssertionError
@@ -33,36 +33,36 @@ private:
     bool checkMeta(Value & v);
 
 public:
-    string attrPath; /* path towards the derivation */
+    std::string attrPath; /* path towards the derivation */
 
     DrvInfo(EvalState & state) : state(&state) { };
-    DrvInfo(EvalState & state, const string & attrPath, Bindings * attrs);
+    DrvInfo(EvalState & state, std::string attrPath, Bindings * attrs);
     DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPathWithOutputs);
 
-    string queryName() const;
+    std::string queryName() const;
-    string querySystem() const;
+    std::string querySystem() const;
-    string queryDrvPath() const;
+    std::string queryDrvPath() const;
-    string queryOutPath() const;
+    std::string queryOutPath() const;
-    string queryOutputName() const;
+    std::string queryOutputName() const;
     /** Return the list of outputs. The "outputs to install" are determined by `meta.outputsToInstall`. */
     Outputs queryOutputs(bool onlyOutputsToInstall = false);
 
     StringSet queryMetaNames();
-    Value * queryMeta(const string & name);
+    Value * queryMeta(const std::string & name);
-    string queryMetaString(const string & name);
+    std::string queryMetaString(const std::string & name);
-    NixInt queryMetaInt(const string & name, NixInt def);
+    NixInt queryMetaInt(const std::string & name, NixInt def);
-    NixFloat queryMetaFloat(const string & name, NixFloat def);
+    NixFloat queryMetaFloat(const std::string & name, NixFloat def);
-    bool queryMetaBool(const string & name, bool def);
+    bool queryMetaBool(const std::string & name, bool def);
-    void setMeta(const string & name, Value * v);
+    void setMeta(const std::string & name, Value * v);
 
     /*
     MetaInfo queryMetaInfo(EvalState & state) const;
     MetaValue queryMetaInfo(EvalState & state, const string & name) const;
     */
 
-    void setName(const string & s) { name = s; }
+    void setName(const std::string & s) { name = s; }
-    void setDrvPath(const string & s) { drvPath = s; }
+    void setDrvPath(const std::string & s) { drvPath = s; }
-    void setOutPath(const string & s) { outPath = s; }
+    void setOutPath(const std::string & s) { outPath = s; }
 
     void setFailed() { failed = true; };
     bool hasFailed() { return failed; };
@@ -81,7 +81,7 @@ typedef std::list<DrvInfo> DrvInfos;
 std::optional<DrvInfo> getDerivation(EvalState & state,
     Value & v, bool ignoreAssertionFailures);
 
-void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
+void getDerivations(EvalState & state, Value & v, const std::string & pathPrefix,
     Bindings & autoArgs, DrvInfos & drvs,
     bool ignoreAssertionFailures);
 

src/libexpr/nixexpr.cc

@@ -16,10 +16,10 @@ std::ostream & operator << (std::ostream & str, const Expr & e)
     return str;
 }
 
-static void showString(std::ostream & str, const string & s)
+static void showString(std::ostream & str, std::string_view s)
 {
     str << '"';
-    for (auto c : (string) s)
+    for (auto c : s)
         if (c == '"' || c == '\\' || c == '$') str << "\\" << c;
         else if (c == '\n') str << "\\n";
         else if (c == '\r') str << "\\r";
@@ -28,7 +28,7 @@ static void showString(std::ostream & str, const string & s)
     str << '"';
 }
 
-static void showId(std::ostream & str, const string & s)
+static void showId(std::ostream & str, std::string_view s)
 {
     if (s.empty())
         str << "\"\"";
@@ -218,7 +218,7 @@ std::ostream & operator << (std::ostream & str, const Pos & pos)
         auto f = format(ANSI_BOLD "%1%" ANSI_NORMAL ":%2%:%3%");
         switch (pos.origin) {
             case foFile:
-                f % (string) pos.file;
+                f % (const std::string &) pos.file;
                 break;
             case foStdin:
             case foString:
@@ -234,7 +234,7 @@ std::ostream & operator << (std::ostream & str, const Pos & pos)
 }
 
 
-string showAttrPath(const AttrPath & attrPath)
+std::string showAttrPath(const AttrPath & attrPath)
 {
     std::ostringstream out;
     bool first = true;
@@ -468,9 +468,9 @@ void ExprLambda::setName(Symbol & name)
 }
 
 
-string ExprLambda::showNamePos() const
+std::string ExprLambda::showNamePos() const
 {
-    return (format("%1% at %2%") % (name.set() ? "'" + (string) name + "'" : "anonymous function") % pos).str();
+    return fmt("%1% at %2%", name.set() ? "'" + (std::string) name + "'" : "anonymous function", pos);
 }
 
 

src/libexpr/nixexpr.hh

@@ -26,18 +26,21 @@ struct Pos
     FileOrigin origin;
     Symbol file;
     unsigned int line, column;
-    Pos() : origin(foString), line(0), column(0) { };
+
+    Pos() : origin(foString), line(0), column(0) { }
     Pos(FileOrigin origin, const Symbol & file, unsigned int line, unsigned int column)
-        : origin(origin), file(file), line(line), column(column) { };
+        : origin(origin), file(file), line(line), column(column) { }
+
     operator bool() const
     {
         return line != 0;
     }
+
     bool operator < (const Pos & p2) const
     {
         if (!line) return p2.line;
         if (!p2.line) return false;
-        int d = ((string) file).compare((string) p2.file);
+        int d = ((const std::string &) file).compare((const std::string &) p2.file);
         if (d < 0) return true;
         if (d > 0) return false;
         if (line < p2.line) return true;
@@ -68,7 +71,7 @@ struct AttrName
 
 typedef std::vector<AttrName> AttrPath;
 
-string showAttrPath(const AttrPath & attrPath);
+std::string showAttrPath(const AttrPath & attrPath);
 
 
 /* Abstract syntax of Nix expressions. */
@@ -110,7 +113,7 @@ struct ExprFloat : Expr
 
 struct ExprString : Expr
 {
-    string s;
+    std::string s;
     Value v;
     ExprString(std::string s) : s(std::move(s)) { v.mkString(this->s.data()); };
     COMMON_METHODS
@@ -119,9 +122,9 @@ struct ExprString : Expr
 
 struct ExprPath : Expr
 {
-    string s;
+    std::string s;
     Value v;
-    ExprPath(const string & s) : s(s) { v.mkPath(this->s.c_str()); };
+    ExprPath(std::string s) : s(std::move(s)) { v.mkPath(this->s.c_str()); };
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env);
 };
@@ -249,7 +252,7 @@ struct ExprLambda : Expr
     {
     };
     void setName(Symbol & name);
-    string showNamePos() const;
+    std::string showNamePos() const;
     inline bool hasFormals() const { return formals != nullptr; }
     COMMON_METHODS
 };

src/libexpr/parser.y

@@ -244,7 +244,7 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
         es2->emplace_back(i->first, e);
     };
     const auto trimString = [&] (const StringToken & t) {
-        string s2;
+        std::string s2;
         for (size_t j = 0; j < t.l; ++j) {
             if (atStartOfLine) {
                 if (t.p[j] == ' ') {
@@ -268,9 +268,9 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols,
         /* Remove the last line if it is empty and consists only of
            spaces. */
         if (n == 1) {
-            string::size_type p = s2.find_last_of('\n');
+            std::string::size_type p = s2.find_last_of('\n');
-            if (p != string::npos && s2.find_first_not_of(' ', p + 1) == string::npos)
+            if (p != std::string::npos && s2.find_first_not_of(' ', p + 1) == std::string::npos)
-                s2 = string(s2, 0, p + 1);
+                s2 = std::string(s2, 0, p + 1);
         }
 
         es2->emplace_back(i->first, new ExprString(s2));
@@ -466,7 +466,7 @@ expr_simple
       $$ = new ExprConcatStrings(CUR_POS, false, $2);
   }
   | SPATH {
-      string path($1.p + 1, $1.l - 2);
+      std::string path($1.p + 1, $1.l - 2);
       $$ = new ExprCall(CUR_POS,
           new ExprVar(data->symbols.create("__findFile")),
           {new ExprVar(data->symbols.create("__nixPath")),
@@ -479,7 +479,7 @@ expr_simple
               .msg = hintfmt("URL literals are disabled"),
               .errPos = CUR_POS
           });
-      $$ = new ExprString(string($1));
+      $$ = new ExprString(std::string($1));
   }
   | '(' expr ')' { $$ = $2; }
   /* Let expressions `let {..., body = ...}' are just desugared
@@ -494,19 +494,19 @@ expr_simple
   ;
 
 string_parts
-  : STR { $$ = new ExprString(string($1)); }
+  : STR { $$ = new ExprString(std::string($1)); }
   | string_parts_interpolated { $$ = new ExprConcatStrings(CUR_POS, true, $1); }
   | { $$ = new ExprString(""); }
   ;
 
 string_parts_interpolated
   : string_parts_interpolated STR
-  { $$ = $1; $1->emplace_back(makeCurPos(@2, data), new ExprString(string($2))); }
+  { $$ = $1; $1->emplace_back(makeCurPos(@2, data), new ExprString(std::string($2))); }
   | string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(makeCurPos(@2, data), $3); }
   | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<Pos, Expr *> >; $$->emplace_back(makeCurPos(@1, data), $2); }
   | STR DOLLAR_CURLY expr '}' {
       $$ = new std::vector<std::pair<Pos, Expr *> >;
-      $$->emplace_back(makeCurPos(@1, data), new ExprString(string($1)));
+      $$->emplace_back(makeCurPos(@1, data), new ExprString(std::string($1)));
       $$->emplace_back(makeCurPos(@2, data), $3);
     }
   ;
@@ -520,7 +520,7 @@ path_start
     $$ = new ExprPath(path);
   }
   | HPATH {
-    Path path(getHome() + string($1.p + 1, $1.l - 1));
+    Path path(getHome() + std::string($1.p + 1, $1.l - 1));
     $$ = new ExprPath(path);
   }
   ;
@@ -738,16 +738,16 @@ Expr * EvalState::parseStdin()
 }
 
 
-void EvalState::addToSearchPath(const string & s)
+void EvalState::addToSearchPath(const std::string & s)
 {
     size_t pos = s.find('=');
-    string prefix;
+    std::string prefix;
     Path path;
-    if (pos == string::npos) {
+    if (pos == std::string::npos) {
         path = s;
     } else {
-        prefix = string(s, 0, pos);
+        prefix = std::string(s, 0, pos);
-        path = string(s, pos + 1);
+        path = std::string(s, pos + 1);
     }
 
     searchPath.emplace_back(prefix, path);

src/libexpr/primops.cc

@@ -141,7 +141,7 @@ static void mkOutputString(
     BindingsBuilder & attrs,
     const StorePath & drvPath,
     const BasicDerivation & drv,
-    const std::pair<string, DerivationOutput> & o)
+    const std::pair<std::string, DerivationOutput> & o)
 {
     auto optOutputPath = o.second.path(*state.store, drv.name, o.first);
     attrs.alloc(o.first).mkString(
@@ -314,7 +314,7 @@ void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value
 {
     auto path = realisePath(state, pos, *args[0]);
 
-    string sym(state.forceStringNoCtx(*args[1], pos));
+    std::string sym(state.forceStringNoCtx(*args[1], pos));
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
     if (!handle)
@@ -386,7 +386,7 @@ void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
 static void prim_typeOf(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
-    string t;
+    std::string t;
     switch (args[0]->type()) {
         case nInt: t = "int"; break;
         case nBool: t = "bool"; break;
@@ -707,7 +707,7 @@ static RegisterPrimOp primop_abort({
     .fun = [](EvalState & state, const Pos & pos, Value * * args, Value & v)
     {
         PathSet context;
-        string s = state.coerceToString(pos, *args[0], context).toOwned();
+        auto s = state.coerceToString(pos, *args[0], context).toOwned();
         throw Abort("evaluation aborted with the following error message: '%1%'", s);
     }
 });
@@ -725,7 +725,7 @@ static RegisterPrimOp primop_throw({
     .fun = [](EvalState & state, const Pos & pos, Value * * args, Value & v)
     {
       PathSet context;
-      string s = state.coerceToString(pos, *args[0], context).toOwned();
+      auto s = state.coerceToString(pos, *args[0], context).toOwned();
       throw ThrownError(s);
     }
 });
@@ -826,7 +826,7 @@ static RegisterPrimOp primop_tryEval({
 /* Return an environment variable.  Use with care. */
 static void prim_getEnv(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    string name(state.forceStringNoCtx(*args[0], pos));
+    std::string name(state.forceStringNoCtx(*args[0], pos));
     v.mkString(evalSettings.restrictEval || evalSettings.pureEval ? "" : getEnv(name).value_or(""));
 }
 
@@ -935,7 +935,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         pos
     );
 
-    string drvName;
+    std::string drvName;
     Pos & posDrvName(*attr->pos);
     try {
         drvName = state.forceStringNoCtx(*attr->value, pos);
@@ -973,7 +973,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 
     for (auto & i : args[0]->attrs->lexicographicOrder()) {
         if (i->name == state.sIgnoreNulls) continue;
-        const string & key = i->name;
+        const std::string & key = i->name;
         vomit("processing attribute '%1%'", key);
 
         auto handleHashMode = [&](const std::string_view s) {
@@ -1031,7 +1031,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             else if (i->name == state.sArgs) {
                 state.forceList(*i->value, pos);
                 for (auto elem : i->value->listItems()) {
-                    string s = state.coerceToString(posDrvName, *elem, context, true).toOwned();
+                    auto s = state.coerceToString(posDrvName, *elem, context, true).toOwned();
                     drv.args.push_back(s);
                 }
             }
@@ -1118,7 +1118,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 
         /* Handle derivation outputs of the form ‘!<name>!<path>’. */
         else if (path.at(0) == '!') {
-            std::pair<string, string> ctx = decodeContext(path);
+            auto ctx = decodeContext(path);
             drv.inputDrvs[state.store->parseStorePath(ctx.first)].insert(ctx.second);
         }
 
@@ -1440,8 +1440,8 @@ static RegisterPrimOp primop_dirOf({
 static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     auto path = realisePath(state, pos, *args[0]);
-    string s = readFile(path);
+    auto s = readFile(path);
-    if (s.find((char) 0) != string::npos)
+    if (s.find((char) 0) != std::string::npos)
         throw Error("the contents of the file '%1%' cannot be represented as a Nix string", path);
     StorePathSet refs;
     if (state.store->isInStore(path)) {
@@ -1474,7 +1474,7 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
     for (auto v2 : args[0]->listItems()) {
         state.forceAttrs(*v2, pos);
 
-        string prefix;
+        std::string prefix;
         Bindings::iterator i = v2->attrs->find(state.sPrefix);
         if (i != v2->attrs->end())
             prefix = state.forceStringNoCtx(*i->value, pos);
@@ -1488,7 +1488,7 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
         );
 
         PathSet context;
-        string path = state.coerceToString(pos, *i->value, context, false, false).toOwned();
+        auto path = state.coerceToString(pos, *i->value, context, false, false).toOwned();
 
         try {
             auto rewrites = state.realiseContext(context);
@@ -1754,8 +1754,8 @@ static RegisterPrimOp primop_fromJSON({
 static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    string name(state.forceStringNoCtx(*args[0], pos));
+    std::string name(state.forceStringNoCtx(*args[0], pos));
-    string contents(state.forceString(*args[1], context, pos));
+    std::string contents(state.forceString(*args[1], context, pos));
 
     StorePathSet refs;
 
@@ -1863,7 +1863,7 @@ static RegisterPrimOp primop_toFile({
 static void addPath(
     EvalState & state,
     const Pos & pos,
-    const string & name,
+    const std::string & name,
     Path path,
     Value * filterFun,
     FileIngestionMethod method,
@@ -2016,14 +2016,14 @@ static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value
 {
     state.forceAttrs(*args[0], pos);
     Path path;
-    string name;
+    std::string name;
     Value * filterFun = nullptr;
     auto method = FileIngestionMethod::Recursive;
     std::optional<Hash> expectedHash;
     PathSet context;
 
     for (auto & attr : *args[0]->attrs) {
-        const string & n(attr.name);
+        auto & n(attr.name);
         if (n == "path")
             path = state.coerceToPath(*attr.pos, *attr.value, context);
         else if (attr.name == state.sName)
@@ -3616,7 +3616,7 @@ static void prim_concatStringsSep(EvalState & state, const Pos & pos, Value * *
     auto sep = state.forceString(*args[0], context, pos);
     state.forceList(*args[1], pos);
 
-    string res;
+    std::string res;
     res.reserve((args[1]->listSize() + 32) * sep.size());
     bool first = true;
 
@@ -3649,12 +3649,12 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
             .errPos = pos
         });
 
-    std::vector<string> from;
+    std::vector<std::string> from;
     from.reserve(args[0]->listSize());
     for (auto elem : args[0]->listItems())
         from.emplace_back(state.forceString(*elem, pos));
 
-    std::vector<std::pair<string, PathSet>> to;
+    std::vector<std::pair<std::string, PathSet>> to;
     to.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
         PathSet ctx;
@@ -3665,7 +3665,7 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
     PathSet context;
     auto s = state.forceString(*args[2], context, pos);
 
-    string res;
+    std::string res;
     // Loops one past last character to handle the case where 'from' contains an empty string.
     for (size_t p = 0; p <= s.size(); ) {
         bool found = false;

src/libexpr/primops/context.cc

@@ -37,7 +37,7 @@ static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & po
 
     PathSet context2;
     for (auto & p : context)
-        context2.insert(p.at(0) == '=' ? string(p, 1) : p);
+        context2.insert(p.at(0) == '=' ? std::string(p, 1) : p);
 
     v.mkString(*s, context2);
 }
@@ -76,13 +76,13 @@ static void prim_getContext(EvalState & state, const Pos & pos, Value * * args,
     auto contextInfos = std::map<Path, ContextInfo>();
     for (const auto & p : context) {
         Path drv;
-        string output;
+        std::string output;
         const Path * path = &p;
         if (p.at(0) == '=') {
-            drv = string(p, 1);
+            drv = std::string(p, 1);
             path = &drv;
         } else if (p.at(0) == '!') {
-            std::pair<string, string> ctx = decodeContext(p);
+            std::pair<std::string, std::string> ctx = decodeContext(p);
             drv = ctx.first;
             output = ctx.second;
             path = &drv;
@@ -166,7 +166,7 @@ static void prim_appendContext(EvalState & state, const Pos & pos, Value * * arg
                         .errPos = *i.pos
                     });
                 }
-                context.insert("=" + string(i.name));
+                context.insert("=" + std::string(i.name));
             }
         }
 

src/libexpr/primops/fetchMercurial.cc

@@ -62,7 +62,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
     fetchers::Attrs attrs;
     attrs.insert_or_assign("type", "hg");
     attrs.insert_or_assign("url", url.find("://") != std::string::npos ? url : "file://" + url);
-    attrs.insert_or_assign("name", string(name));
+    attrs.insert_or_assign("name", std::string(name));
     if (ref) attrs.insert_or_assign("ref", *ref);
     if (rev) attrs.insert_or_assign("rev", rev->gitRev());
     auto input = fetchers::Input::fromAttrs(std::move(attrs));

src/libexpr/primops/fetchTree.cc

@@ -186,7 +186,7 @@ static void prim_fetchTree(EvalState & state, const Pos & pos, Value * * args, V
 static RegisterPrimOp primop_fetchTree("fetchTree", 1, prim_fetchTree);
 
 static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
-    const string & who, bool unpack, std::string name)
+    const std::string & who, bool unpack, std::string name)
 {
     std::optional<std::string> url;
     std::optional<Hash> expectedHash;
@@ -198,7 +198,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
         state.forceAttrs(*args[0], pos);
 
         for (auto & attr : *args[0]->attrs) {
-            string n(attr.name);
+            std::string n(attr.name);
             if (n == "url")
                 url = state.forceStringNoCtx(*attr.value, *attr.pos);
             else if (n == "sha256")

src/libexpr/primops/fromTOML.cc

@@ -9,7 +9,7 @@ static void prim_fromTOML(EvalState & state, const Pos & pos, Value * * args, Va
 {
     auto toml = state.forceStringNoCtx(*args[0], pos);
 
-    std::istringstream tomlStream(string{toml});
+    std::istringstream tomlStream(std::string{toml});
 
     std::function<void(Value &, toml::value)> visit;
 

src/libexpr/value-to-xml.cc

@@ -9,7 +9,7 @@
 namespace nix {
 
 
-static XMLAttrs singletonAttrs(const string & name, const string & value)
+static XMLAttrs singletonAttrs(const std::string & name, const std::string & value)
 {
     XMLAttrs attrs;
     attrs[name] = value;

src/libfetchers/mercurial.cc

@@ -26,7 +26,7 @@ static RunOptions hgOptions(const Strings & args)
 }
 
 // runProgram wrapper that uses hgOptions instead of stock RunOptions.
-static string runHg(const Strings & args, const std::optional<std::string> & input = {})
+static std::string runHg(const Strings & args, const std::optional<std::string> & input = {})
 {
     RunOptions opts = hgOptions(args);
     opts.input = input;
@@ -254,7 +254,7 @@ struct MercurialInputScheme : InputScheme
                     runHg({ "pull", "-R", cacheDir, "--", actualUrl });
                 }
                 catch (ExecError & e) {
-                    string transJournal = cacheDir + "/.hg/store/journal";
+                    auto transJournal = cacheDir + "/.hg/store/journal";
                     /* hg throws "abandoned transaction" error only if this file exists */
                     if (pathExists(transJournal)) {
                         runHg({ "recover", "-R", cacheDir });

src/libmain/common-args.cc

@@ -4,7 +4,7 @@
 
 namespace nix {
 
-MixCommonArgs::MixCommonArgs(const string & programName)
+MixCommonArgs::MixCommonArgs(const std::string & programName)
     : programName(programName)
 {
     addFlag({

src/libmain/common-args.hh

@@ -11,8 +11,8 @@ class MixCommonArgs : public virtual Args
 {
     void initialFlagsProcessed() override;
 public:
-    string programName;
+    std::string programName;
-    MixCommonArgs(const string & programName);
+    MixCommonArgs(const std::string & programName);
 protected:
     virtual void pluginsInited() {}
 };

src/libmain/shared.cc

@@ -94,7 +94,7 @@ void printMissing(ref<Store> store, const StorePathSet & willBuild,
 }
 
 
-string getArg(const string & opt,
+std::string getArg(const std::string & opt,
     Strings::iterator & i, const Strings::iterator & end)
 {
     ++i;
@@ -227,6 +227,8 @@ LegacyArgs::LegacyArgs(const std::string & programName,
     std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg)
     : MixCommonArgs(programName), parseArg(parseArg)
 {
+    printError("FOO %s", programName);
+    
     addFlag({
         .longName = "no-build-output",
         .shortName = 'Q',
@@ -322,14 +324,14 @@ void parseCmdLine(int argc, char * * argv,
 }
 
 
-void parseCmdLine(const string & programName, const Strings & args,
+void parseCmdLine(const std::string & programName, const Strings & args,
     std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg)
 {
     LegacyArgs(programName, parseArg).parseCmdline(args);
 }
 
 
-void printVersion(const string & programName)
+void printVersion(const std::string & programName)
 {
     std::cout << format("%1% (Nix) %2%") % programName % nixVersion << std::endl;
     if (verbosity > lvlInfo) {
@@ -352,7 +354,7 @@ void printVersion(const string & programName)
 }
 
 
-void showManPage(const string & name)
+void showManPage(const std::string & name)
 {
     restoreProcessContext();
     setenv("MANPATH", settings.nixManDir.c_str(), 1);
@@ -361,13 +363,13 @@ void showManPage(const string & name)
 }
 
 
-int handleExceptions(const string & programName, std::function<void()> fun)
+int handleExceptions(const std::string & programName, std::function<void()> fun)
 {
     ReceiveInterrupts receiveInterrupts; // FIXME: need better place for this
 
     ErrorInfo::programName = baseNameOf(programName);
 
-    string error = ANSI_RED "error:" ANSI_NORMAL " ";
+    std::string error = ANSI_RED "error:" ANSI_NORMAL " ";
     try {
         try {
             fun();
@@ -407,7 +409,7 @@ RunPager::RunPager()
     if (!isatty(STDOUT_FILENO)) return;
     char * pager = getenv("NIX_PAGER");
     if (!pager) pager = getenv("PAGER");
-    if (pager && ((string) pager == "" || (string) pager == "cat")) return;
+    if (pager && ((std::string) pager == "" || (std::string) pager == "cat")) return;
 
     Pipe toPager;
     toPager.create();

src/libmain/shared.hh

@@ -22,7 +22,7 @@ public:
     virtual ~Exit();
 };
 
-int handleExceptions(const string & programName, std::function<void()> fun);
+int handleExceptions(const std::string & programName, std::function<void()> fun);
 
 /* Don't forget to call initPlugins() after settings are initialized! */
 void initNix();
@@ -30,10 +30,10 @@ void initNix();
 void parseCmdLine(int argc, char * * argv,
     std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg);
 
-void parseCmdLine(const string & programName, const Strings & args,
+void parseCmdLine(const std::string & programName, const Strings & args,
     std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg);
 
-void printVersion(const string & programName);
+void printVersion(const std::string & programName);
 
 /* Ugh.  No better place to put this. */
 void printGCWarning();
@@ -50,10 +50,10 @@ void printMissing(ref<Store> store, const StorePathSet & willBuild,
     const StorePathSet & willSubstitute, const StorePathSet & unknown,
     uint64_t downloadSize, uint64_t narSize, Verbosity lvl = lvlInfo);
 
-string getArg(const string & opt,
+std::string getArg(const std::string & opt,
     Strings::iterator & i, const Strings::iterator & end);
 
-template<class N> N getIntArg(const string & opt,
+template<class N> N getIntArg(const std::string & opt,
     Strings::iterator & i, const Strings::iterator & end, bool allowUnit)
 {
     ++i;
@@ -76,7 +76,7 @@ struct LegacyArgs : public MixCommonArgs
 
 
 /* Show the manual page for the specified program. */
-void showManPage(const string & name);
+void showManPage(const std::string & name);
 
 /* The constructor of this class starts a pager if stdout is a
    terminal and $PAGER is set. Stdout is redirected to the pager. */
@@ -96,7 +96,7 @@ extern volatile ::sig_atomic_t blockInt;
 
 /* GC helpers. */
 
-string showBytes(uint64_t bytes);
+std::string showBytes(uint64_t bytes);
 
 struct GCResults;
 

src/libstore/binary-cache-store.cc

@@ -385,8 +385,14 @@ void BinaryCacheStore::queryPathInfoUncached(const StorePath & storePath,
         }});
 }
 
-StorePath BinaryCacheStore::addToStore(const string & name, const Path & srcPath,
+StorePath BinaryCacheStore::addToStore(
-    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair, const StorePathSet & references)
+    std::string_view name,
+    const Path & srcPath,
+    FileIngestionMethod method,
+    HashType hashAlgo,
+    PathFilter & filter,
+    RepairFlag repair,
+    const StorePathSet & references)
 {
     /* FIXME: Make BinaryCacheStore::addToStoreCommon support
        non-recursive+sha256 so we can just use the default
@@ -418,8 +424,11 @@ StorePath BinaryCacheStore::addToStore(const string & name, const Path & srcPath
     })->path;
 }
 
-StorePath BinaryCacheStore::addTextToStore(const string & name, const string & s,
+StorePath BinaryCacheStore::addTextToStore(
-    const StorePathSet & references, RepairFlag repair)
+    std::string_view name,
+    std::string_view s,
+    const StorePathSet & references,
+    RepairFlag repair)
 {
     auto textHash = hashString(htSHA256, s);
     auto path = makeTextPath(name, textHash, references);

src/libstore/binary-cache-store.hh

@@ -101,12 +101,20 @@ public:
     StorePath addToStoreFromDump(Source & dump, std::string_view name,
         FileIngestionMethod method, HashType hashAlgo, RepairFlag repair, const StorePathSet & references) override;
 
-    StorePath addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(
-        FileIngestionMethod method, HashType hashAlgo,
+        std::string_view name,
-        PathFilter & filter, RepairFlag repair, const StorePathSet & references) override;
+        const Path & srcPath,
+        FileIngestionMethod method,
+        HashType hashAlgo,
+        PathFilter & filter,
+        RepairFlag repair,
+        const StorePathSet & references) override;
 
-    StorePath addTextToStore(const string & name, const string & s,
+    StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair) override;
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair) override;
 
     void registerDrvOutput(const Realisation & info) override;
 

src/libstore/build/derivation-goal.cc

@@ -116,7 +116,7 @@ DerivationGoal::~DerivationGoal()
 }
 
 
-string DerivationGoal::key()
+std::string DerivationGoal::key()
 {
     /* Ensure that derivations get built in order of their name,
        i.e. a derivation named "aardvark" always comes before
@@ -1013,7 +1013,7 @@ HookReply DerivationGoal::tryBuildHook()
 
         /* Read the first line of input, which should be a word indicating
            whether the hook wishes to perform the build. */
-        string reply;
+        std::string reply;
         while (true) {
             auto s = [&]() {
                 try {
@@ -1025,8 +1025,8 @@ HookReply DerivationGoal::tryBuildHook()
             }();
             if (handleJSONLogMessage(s, worker.act, worker.hook->activities, true))
                 ;
-            else if (string(s, 0, 2) == "# ") {
+            else if (s.substr(0, 2) == "# ") {
-                reply = string(s, 2);
+                reply = s.substr(2);
                 break;
             }
             else {
@@ -1140,10 +1140,10 @@ Path DerivationGoal::openLogFile()
         logDir = localStore->logDir;
     else
         logDir = settings.nixLogDir;
-    Path dir = fmt("%s/%s/%s/", logDir, LocalFSStore::drvsLogDir, string(baseName, 0, 2));
+    Path dir = fmt("%s/%s/%s/", logDir, LocalFSStore::drvsLogDir, baseName.substr(0, 2));
     createDirs(dir);
 
-    Path logFileName = fmt("%s/%s%s", dir, string(baseName, 2),
+    Path logFileName = fmt("%s/%s%s", dir, baseName.substr(2),
         settings.compressLog ? ".bz2" : "");
 
     fdLogFile = open(logFileName.c_str(), O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC, 0666);
@@ -1176,7 +1176,7 @@ bool DerivationGoal::isReadDesc(int fd)
 }
 
 
-void DerivationGoal::handleChildOutput(int fd, const string & data)
+void DerivationGoal::handleChildOutput(int fd, std::string_view data)
 {
     if (isReadDesc(fd))
     {

src/libstore/build/derivation-goal.hh

@@ -145,7 +145,7 @@ struct DerivationGoal : public Goal
 
     void timedOut(Error && ex) override;
 
-    string key() override;
+    std::string key() override;
 
     void work() override;
 
@@ -200,7 +200,7 @@ struct DerivationGoal : public Goal
     virtual bool isReadDesc(int fd);
 
     /* Callback used by the worker to write to the log. */
-    void handleChildOutput(int fd, const string & data) override;
+    void handleChildOutput(int fd, std::string_view data) override;
     void handleEOF(int fd) override;
     void flushLine();
 

src/libstore/build/drv-output-substitution-goal.cc

@@ -137,7 +137,7 @@ void DrvOutputSubstitutionGoal::finished()
     amDone(ecSuccess);
 }
 
-string DrvOutputSubstitutionGoal::key()
+std::string DrvOutputSubstitutionGoal::key()
 {
     /* "a$" ensures substitution goals happen before derivation
        goals. */

src/libstore/build/drv-output-substitution-goal.hh

@@ -51,7 +51,7 @@ public:
 
     void timedOut(Error && ex) override { abort(); };
 
-    string key() override;
+    std::string key() override;
 
     void work() override;
     void handleEOF(int fd) override;

src/libstore/build/goal.cc

@@ -5,8 +5,8 @@ namespace nix {
 
 
 bool CompareGoalPtrs::operator() (const GoalPtr & a, const GoalPtr & b) const {
-    string s1 = a->key();
+    std::string s1 = a->key();
-    string s2 = b->key();
+    std::string s2 = b->key();
     return s1 < s2;
 }
 

src/libstore/build/goal.hh

@@ -50,7 +50,7 @@ struct Goal : public std::enable_shared_from_this<Goal>
     unsigned int nrIncompleteClosure;
 
     /* Name of this goal for debugging purposes. */
-    string name;
+    std::string name;
 
     /* Whether the goal is finished. */
     ExitCode exitCode;
@@ -75,7 +75,7 @@ struct Goal : public std::enable_shared_from_this<Goal>
 
     virtual void waiteeDone(GoalPtr waitee, ExitCode result);
 
-    virtual void handleChildOutput(int fd, const string & data)
+    virtual void handleChildOutput(int fd, std::string_view data)
     {
         abort();
     }
@@ -87,7 +87,7 @@ struct Goal : public std::enable_shared_from_this<Goal>
 
     void trace(const FormatOrString & fs);
 
-    string getName()
+    std::string getName()
     {
         return name;
     }
@@ -97,7 +97,7 @@ struct Goal : public std::enable_shared_from_this<Goal>
        by the worker (important!), etc. */
     virtual void timedOut(Error && ex) = 0;
 
-    virtual string key() = 0;
+    virtual std::string key() = 0;
 
     void amDone(ExitCode result, std::optional<Error> ex = {});
 

src/libstore/build/local-derivation-goal.cc

@@ -481,12 +481,12 @@ void LocalDerivationGoal::startBuilder()
            temporary build directory.  The text files have the format used
            by `nix-store --register-validity'.  However, the deriver
            fields are left empty. */
-        string s = get(drv->env, "exportReferencesGraph").value_or("");
+        auto s = get(drv->env, "exportReferencesGraph").value_or("");
         Strings ss = tokenizeString<Strings>(s);
         if (ss.size() % 2 != 0)
             throw BuildError("odd number of tokens in 'exportReferencesGraph': '%1%'", s);
         for (Strings::iterator i = ss.begin(); i != ss.end(); ) {
-            string fileName = *i++;
+            auto fileName = *i++;
             static std::regex regex("[A-Za-z_][A-Za-z0-9_.-]*");
             if (!std::regex_match(fileName, regex))
                 throw Error("invalid file name '%s' in 'exportReferencesGraph'", fileName);
@@ -517,10 +517,10 @@ void LocalDerivationGoal::startBuilder()
                 i.pop_back();
             }
             size_t p = i.find('=');
-            if (p == string::npos)
+            if (p == std::string::npos)
                 dirsInChroot[i] = {i, optional};
             else
-                dirsInChroot[string(i, 0, p)] = {string(i, p + 1), optional};
+                dirsInChroot[i.substr(0, p)] = {i.substr(p + 1), optional};
         }
         dirsInChroot[tmpDirInSandbox] = tmpDir;
 
@@ -671,9 +671,10 @@ void LocalDerivationGoal::startBuilder()
         auto state = stBegin;
         auto lines = runProgram(settings.preBuildHook, false, args);
         auto lastPos = std::string::size_type{0};
-        for (auto nlPos = lines.find('\n'); nlPos != string::npos;
+        for (auto nlPos = lines.find('\n'); nlPos != std::string::npos;
-                nlPos = lines.find('\n', lastPos)) {
+                nlPos = lines.find('\n', lastPos))
-            auto line = std::string{lines, lastPos, nlPos - lastPos};
+        {
+            auto line = lines.substr(lastPos, nlPos - lastPos);
             lastPos = nlPos + 1;
             if (state == stBegin) {
                 if (line == "extra-sandbox-paths" || line == "extra-chroot-dirs") {
@@ -686,10 +687,10 @@ void LocalDerivationGoal::startBuilder()
                     state = stBegin;
                 } else {
                     auto p = line.find('=');
-                    if (p == string::npos)
+                    if (p == std::string::npos)
                         dirsInChroot[line] = line;
                     else
-                        dirsInChroot[string(line, 0, p)] = string(line, p + 1);
+                        dirsInChroot[line.substr(0, p)] = line.substr(p + 1);
                 }
             }
         }
@@ -941,7 +942,7 @@ void LocalDerivationGoal::startBuilder()
     /* Check if setting up the build environment failed. */
     std::vector<std::string> msgs;
     while (true) {
-        string msg = [&]() {
+        std::string msg = [&]() {
             try {
                 return readLine(builderOut.readSide.get());
             } catch (Error & e) {
@@ -953,8 +954,8 @@ void LocalDerivationGoal::startBuilder()
                 throw;
             }
         }();
-        if (string(msg, 0, 1) == "\2") break;
+        if (msg.substr(0, 1) == "\2") break;
-        if (string(msg, 0, 1) == "\1") {
+        if (msg.substr(0, 1) == "\1") {
             FdSource source(builderOut.readSide.get());
             auto ex = readError(source);
             ex.addTrace({}, "while setting up the build environment");
@@ -990,7 +991,7 @@ void LocalDerivationGoal::initTmpDir() {
                 env[i.first] = i.second;
             } else {
                 auto hash = hashString(htSHA256, i.first);
-                string fn = ".attr-" + hash.to_string(Base32, false);
+                std::string fn = ".attr-" + hash.to_string(Base32, false);
                 Path p = tmpDir + "/" + fn;
                 writeFile(p, rewriteStrings(i.second, inputRewrites));
                 chownToBuilder(p);
@@ -1081,7 +1082,7 @@ void LocalDerivationGoal::writeStructuredAttrs()
         for (auto & [i, v] : json["outputs"].get<nlohmann::json::object_t>()) {
             /* The placeholder must have a rewrite, so we use it to cover both the
                cases where we know or don't know the output path ahead of time. */
-            rewritten[i] = rewriteStrings(v, inputRewrites);
+            rewritten[i] = rewriteStrings((std::string) v, inputRewrites);
         }
 
         json["outputs"] = rewritten;
@@ -1187,10 +1188,14 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
     std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
     { throw Error("queryPathFromHashPart"); }
 
-    StorePath addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
+        std::string_view name,
-        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair,
+        const Path & srcPath,
-        const StorePathSet & references = StorePathSet()) override
+        FileIngestionMethod method,
+        HashType hashAlgo,
+        PathFilter & filter,
+        RepairFlag repair,
+        const StorePathSet & references) override
     { throw Error("addToStore"); }
 
     void addToStore(const ValidPathInfo & info, Source & narSource,
@@ -1200,17 +1205,24 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
         goal.addDependency(info.path);
     }
 
-    StorePath addTextToStore(const string & name, const string & s,
+    StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair = NoRepair) override
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair = NoRepair) override
     {
         auto path = next->addTextToStore(name, s, references, repair);
         goal.addDependency(path);
         return path;
     }
 
-    StorePath addToStoreFromDump(Source & dump, std::string_view name,
+    StorePath addToStoreFromDump(
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair,
+        Source & dump,
-        const StorePathSet & references = StorePathSet()) override
+        std::string_view name,
+        FileIngestionMethod method,
+        HashType hashAlgo,
+        RepairFlag repair,
+        const StorePathSet & references) override
     {
         auto path = next->addToStoreFromDump(dump, name, method, hashAlgo, repair, references);
         goal.addDependency(path);
@@ -1992,7 +2004,7 @@ void LocalDerivationGoal::runChild()
             args.push_back(rewriteStrings(i, inputRewrites));
 
         /* Indicate that we managed to set up the build environment. */
-        writeFull(STDERR_FILENO, string("\2\n"));
+        writeFull(STDERR_FILENO, std::string("\2\n"));
 
         /* Execute the program.  This should not return. */
         if (drv->isBuiltin()) {
@@ -2010,7 +2022,7 @@ void LocalDerivationGoal::runChild()
                 else if (drv->builder == "builtin:unpack-channel")
                     builtinUnpackChannel(drv2);
                 else
-                    throw Error("unsupported builtin builder '%1%'", string(drv->builder, 8));
+                    throw Error("unsupported builtin builder '%1%'", drv->builder.substr(8));
                 _exit(0);
             } catch (std::exception & e) {
                 writeFull(STDERR_FILENO, e.what() + std::string("\n"));
@@ -2694,7 +2706,7 @@ void LocalDerivationGoal::checkOutputs(const std::map<Path, ValidPathInfo> & out
                     }
 
                 if (!badPaths.empty()) {
-                    string badPathsStr;
+                    std::string badPathsStr;
                     for (auto & i : badPaths) {
                         badPathsStr += "\n  ";
                         badPathsStr += worker.store.printStorePath(i);

src/libstore/build/local-derivation-goal.hh

@@ -58,7 +58,7 @@ struct LocalDerivationGoal : public DerivationGoal
     typedef map<Path, ChrootPath> DirsInChroot; // maps target path to source path
     DirsInChroot dirsInChroot;
 
-    typedef map<string, string> Environment;
+    typedef map<std::string, std::string> Environment;
     Environment env;
 
 #if __APPLE__

src/libstore/build/substitution-goal.cc

@@ -272,7 +272,7 @@ void PathSubstitutionGoal::finished()
 }
 
 
-void PathSubstitutionGoal::handleChildOutput(int fd, const string & data)
+void PathSubstitutionGoal::handleChildOutput(int fd, std::string_view data)
 {
 }
 

src/libstore/build/substitution-goal.hh

@@ -59,7 +59,7 @@ public:
 
     void timedOut(Error && ex) override { abort(); };
 
-    string key() override
+    std::string key() override
     {
         /* "a$" ensures substitution goals happen before derivation
            goals. */
@@ -77,7 +77,7 @@ public:
     void finished();
 
     /* Callback used by the worker to write to the log. */
-    void handleChildOutput(int fd, const string & data) override;
+    void handleChildOutput(int fd, std::string_view data) override;
     void handleEOF(int fd) override;
 
     void cleanup() override;

src/libstore/build/worker.cc

@@ -394,7 +394,7 @@ void Worker::waitForInput()
                 } else {
                     printMsg(lvlVomit, "%1%: read %2% bytes",
                         goal->getName(), rd);
-                    string data((char *) buffer.data(), rd);
+                    std::string data((char *) buffer.data(), rd);
                     j->lastOutput = after;
                     goal->handleChildOutput(k, data);
                 }

src/libstore/builtins/buildenv.cc

@@ -123,7 +123,7 @@ void buildProfile(const Path & out, Packages && pkgs)
         createLinks(state, pkgDir, out, priority);
 
         try {
-            for (const auto & p : tokenizeString<std::vector<string>>(
+            for (const auto & p : tokenizeString<std::vector<std::string>>(
                     readFile(pkgDir + "/nix-support/propagated-user-env-packages"), " \n"))
                 if (!done.count(p))
                     postponed.insert(p);
@@ -161,7 +161,7 @@ void buildProfile(const Path & out, Packages && pkgs)
 
 void builtinBuildenv(const BasicDerivation & drv)
 {
-    auto getAttr = [&](const string & name) {
+    auto getAttr = [&](const std::string & name) {
         auto i = drv.env.find(name);
         if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
         return i->second;

src/libstore/builtins/fetchurl.cc

@@ -16,7 +16,7 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
         writeFile(settings.netrcFile, netrcData, 0600);
     }
 
-    auto getAttr = [&](const string & name) {
+    auto getAttr = [&](const std::string & name) {
         auto i = drv.env.find(name);
         if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
         return i->second;

src/libstore/builtins/unpack-channel.cc

@@ -5,7 +5,7 @@ namespace nix {
 
 void builtinUnpackChannel(const BasicDerivation & drv)
 {
-    auto getAttr = [&](const string & name) {
+    auto getAttr = [&](const std::string & name) {
         auto i = drv.env.find(name);
         if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
         return i->second;

src/libstore/daemon.cc

@@ -479,8 +479,8 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopAddTextToStore: {
-        string suffix = readString(from);
+        std::string suffix = readString(from);
-        string s = readString(from);
+        std::string s = readString(from);
         auto refs = worker_proto::read(*store, from, Phantom<StorePathSet> {});
         logger->startWork();
         auto path = store->addTextToStore(suffix, s, refs, NoRepair);
@@ -698,8 +698,8 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (GET_PROTOCOL_MINOR(clientVersion) >= 12) {
             unsigned int n = readInt(from);
             for (unsigned int i = 0; i < n; i++) {
-                string name = readString(from);
+                auto name = readString(from);
-                string value = readString(from);
+                auto value = readString(from);
                 clientSettings.overrides.emplace(name, value);
             }
         }

src/libstore/derivations.cc

@@ -82,7 +82,7 @@ bool derivationIsImpure(DerivationType dt) {
 
 bool BasicDerivation::isBuiltin() const
 {
-    return string(builder, 0, 8) == "builtin:";
+    return builder.substr(0, 8) == "builtin:";
 }
 
 
@@ -104,19 +104,19 @@ StorePath writeDerivation(Store & store,
 
 
 /* Read string `s' from stream `str'. */
-static void expect(std::istream & str, const string & s)
+static void expect(std::istream & str, std::string_view s)
 {
     char s2[s.size()];
     str.read(s2, s.size());
-    if (string(s2, s.size()) != s)
+    if (std::string(s2, s.size()) != s)
         throw FormatError("expected string '%1%'", s);
 }
 
 
 /* Read a C-style string from stream `str'. */
-static string parseString(std::istream & str)
+static std::string parseString(std::istream & str)
 {
-    string res;
+    std::string res;
     expect(str, "\"");
     int c;
     while ((c = str.get()) != '"')
@@ -172,7 +172,7 @@ static DerivationOutput parseDerivationOutput(const Store & store,
 {
     if (hashAlgo != "") {
         auto method = FileIngestionMethod::Flat;
-        if (string(hashAlgo, 0, 2) == "r:") {
+        if (hashAlgo.substr(0, 2) == "r:") {
             method = FileIngestionMethod::Recursive;
             hashAlgo = hashAlgo.substr(2);
         }
@@ -260,8 +260,8 @@ Derivation parseDerivation(const Store & store, std::string && s, std::string_vi
     /* Parse the environment variables. */
     expect(str, ",[");
     while (!endOfList(str)) {
-        expect(str, "("); string name = parseString(str);
+        expect(str, "("); auto name = parseString(str);
-        expect(str, ","); string value = parseString(str);
+        expect(str, ","); auto value = parseString(str);
         expect(str, ")");
         drv.env[name] = value;
     }
@@ -271,7 +271,7 @@ Derivation parseDerivation(const Store & store, std::string && s, std::string_vi
 }
 
 
-static void printString(string & res, std::string_view s)
+static void printString(std::string & res, std::string_view s)
 {
     boost::container::small_vector<char, 64 * 1024> buffer;
     buffer.reserve(s.size() * 2 + 2);
@@ -289,7 +289,7 @@ static void printString(string & res, std::string_view s)
 }
 
 
-static void printUnquotedString(string & res, std::string_view s)
+static void printUnquotedString(std::string & res, std::string_view s)
 {
     res += '"';
     res.append(s);
@@ -298,7 +298,7 @@ static void printUnquotedString(string & res, std::string_view s)
 
 
 template<class ForwardIterator>
-static void printStrings(string & res, ForwardIterator i, ForwardIterator j)
+static void printStrings(std::string & res, ForwardIterator i, ForwardIterator j)
 {
     res += '[';
     bool first = true;
@@ -311,7 +311,7 @@ static void printStrings(string & res, ForwardIterator i, ForwardIterator j)
 
 
 template<class ForwardIterator>
-static void printUnquotedStrings(string & res, ForwardIterator i, ForwardIterator j)
+static void printUnquotedStrings(std::string & res, ForwardIterator i, ForwardIterator j)
 {
     res += '[';
     bool first = true;
@@ -323,10 +323,10 @@ static void printUnquotedStrings(string & res, ForwardIterator i, ForwardIterato
 }
 
 
-string Derivation::unparse(const Store & store, bool maskOutputs,
+std::string Derivation::unparse(const Store & store, bool maskOutputs,
     std::map<std::string, StringSet> * actualInputs) const
 {
-    string s;
+    std::string s;
     s.reserve(65536);
     s += "Derive([";
 
@@ -401,7 +401,7 @@ string Derivation::unparse(const Store & store, bool maskOutputs,
 
 
 // FIXME: remove
-bool isDerivation(const string & fileName)
+bool isDerivation(const std::string & fileName)
 {
     return hasSuffix(fileName, drvExtension);
 }
@@ -593,7 +593,7 @@ std::map<std::string, Hash> staticOutputHashes(Store & store, const Derivation &
 }
 
 
-bool wantOutput(const string & output, const std::set<string> & wanted)
+bool wantOutput(const std::string & output, const std::set<std::string> & wanted)
 {
     return wanted.empty() || wanted.find(output) != wanted.end();
 }

src/libstore/derivations.hh

@@ -59,21 +59,19 @@ struct DerivationOutput
     std::optional<StorePath> path(const Store & store, std::string_view drvName, std::string_view outputName) const;
 };
 
-typedef std::map<string, DerivationOutput> DerivationOutputs;
+typedef std::map<std::string, DerivationOutput> DerivationOutputs;
 
 /* These are analogues to the previous DerivationOutputs data type, but they
    also contains, for each output, the (optional) store path in which it would
    be written. To calculate values of these types, see the corresponding
    functions in BasicDerivation */
-typedef std::map<string, std::pair<DerivationOutput, std::optional<StorePath>>>
+typedef std::map<std::string, std::pair<DerivationOutput, std::optional<StorePath>>>
   DerivationOutputsAndOptPaths;
 
 /* For inputs that are sub-derivations, we specify exactly which
    output IDs we are interested in. */
 typedef std::map<StorePath, StringSet> DerivationInputs;
 
-typedef std::map<string, string> StringPairs;
-
 enum struct DerivationType : uint8_t {
     InputAddressed,
     DeferredInputAddressed,
@@ -103,7 +101,7 @@ struct BasicDerivation
 {
     DerivationOutputs outputs; /* keyed on symbolic IDs */
     StorePathSet inputSrcs; /* inputs that are sources */
-    string platform;
+    std::string platform;
     Path builder;
     Strings args;
     StringPairs env;
@@ -164,7 +162,7 @@ StorePath writeDerivation(Store & store,
 Derivation parseDerivation(const Store & store, std::string && s, std::string_view name);
 
 // FIXME: remove
-bool isDerivation(const string & fileName);
+bool isDerivation(const std::string & fileName);
 
 /* Calculate the name that will be used for the store path for this
    output.
@@ -222,7 +220,7 @@ typedef std::map<StorePath, DrvHashModulo> DrvHashes;
 // FIXME: global, though at least thread-safe.
 extern Sync<DrvHashes> drvHashes;
 
-bool wantOutput(const string & output, const std::set<string> & wanted);
+bool wantOutput(const std::string & output, const std::set<std::string> & wanted);
 
 struct Source;
 struct Sink;

src/libstore/derived-path.cc

@@ -75,9 +75,9 @@ DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_vi
     assert(n != s.npos);
     auto drvPath = store.parseStorePath(s.substr(0, n));
     auto outputsS = s.substr(n + 1);
-    std::set<string> outputs;
+    std::set<std::string> outputs;
     if (outputsS != "*")
-        outputs = tokenizeString<std::set<string>>(outputsS, ",");
+        outputs = tokenizeString<std::set<std::string>>(outputsS, ",");
     return {drvPath, outputs};
 }
 

src/libstore/dummy-store.cc

@@ -21,7 +21,7 @@ struct DummyStore : public virtual DummyStoreConfig, public virtual Store
         , Store(params)
     { }
 
-    string getUri() override
+    std::string getUri() override
     {
         return *uriSchemes().begin();
     }
@@ -43,8 +43,11 @@ struct DummyStore : public virtual DummyStoreConfig, public virtual Store
         RepairFlag repair, CheckSigsFlag checkSigs) override
     { unsupported("addToStore"); }
 
-    StorePath addTextToStore(const string & name, const string & s,
+    StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair) override
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair) override
     { unsupported("addTextToStore"); }
 
     void narFromPath(const StorePath & path, Sink & sink) override

src/libstore/filetransfer.cc

@@ -33,12 +33,12 @@ FileTransferSettings fileTransferSettings;
 
 static GlobalConfig::Register rFileTransferSettings(&fileTransferSettings);
 
-std::string resolveUri(const std::string & uri)
+std::string resolveUri(std::string_view uri)
 {
     if (uri.compare(0, 8, "channel:") == 0)
-        return "https://nixos.org/channels/" + std::string(uri, 8) + "/nixexprs.tar.xz";
+        return "https://nixos.org/channels/" + std::string(uri.substr(8)) + "/nixexprs.tar.xz";
     else
-        return uri;
+        return std::string(uri);
 }
 
 struct curlFileTransfer : public FileTransfer
@@ -197,15 +197,15 @@ struct curlFileTransfer : public FileTransfer
                 result.etag = "";
                 result.data.clear();
                 result.bodySize = 0;
-                statusMsg = trim(match[1]);
+                statusMsg = trim((std::string &) match[1]);
                 acceptRanges = false;
                 encoding = "";
             } else {
                 auto i = line.find(':');
-                if (i != string::npos) {
+                if (i != std::string::npos) {
-                    string name = toLower(trim(string(line, 0, i)));
+                    std::string name = toLower(trim(line.substr(0, i)));
                     if (name == "etag") {
-                        result.etag = trim(string(line, i + 1));
+                        result.etag = trim(line.substr(i + 1));
                         /* Hack to work around a GitHub bug: it sends
                            ETags, but ignores If-None-Match. So if we get
                            the expected ETag on a 200 response, then shut
@@ -218,8 +218,8 @@ struct curlFileTransfer : public FileTransfer
                             return 0;
                         }
                     } else if (name == "content-encoding")
-                        encoding = trim(string(line, i + 1));
+                        encoding = trim(line.substr(i + 1));
-                    else if (name == "accept-ranges" && toLower(trim(std::string(line, i + 1))) == "bytes")
+                    else if (name == "accept-ranges" && toLower(trim(line.substr(i + 1))) == "bytes")
                         acceptRanges = true;
                 }
             }
@@ -866,18 +866,18 @@ FileTransferError::FileTransferError(FileTransfer::Error error, std::optional<st
     // FIXME: Due to https://github.com/NixOS/nix/issues/3841 we don't know how
     // to print different messages for different verbosity levels. For now
     // we add some heuristics for detecting when we want to show the response.
-    if (response && (response->size() < 1024 || response->find("<html>") != string::npos))
+    if (response && (response->size() < 1024 || response->find("<html>") != std::string::npos))
         err.msg = hintfmt("%1%\n\nresponse body:\n\n%2%", normaltxt(hf.str()), chomp(*response));
     else
         err.msg = hf;
 }
 
-bool isUri(const string & s)
+bool isUri(std::string_view s)
 {
     if (s.compare(0, 8, "channel:") == 0) return true;
     size_t pos = s.find("://");
-    if (pos == string::npos) return false;
+    if (pos == std::string::npos) return false;
-    string scheme(s, 0, pos);
+    std::string scheme(s, 0, pos);
     return scheme == "http" || scheme == "https" || scheme == "file" || scheme == "channel" || scheme == "git" || scheme == "s3" || scheme == "ssh";
 }
 

src/libstore/filetransfer.hh

@@ -119,17 +119,17 @@ class FileTransferError : public Error
 {
 public:
     FileTransfer::Error error;
-    std::optional<string> response; // intentionally optional
+    std::optional<std::string> response; // intentionally optional
 
     template<typename... Args>
-    FileTransferError(FileTransfer::Error error, std::optional<string> response, const Args & ... args);
+    FileTransferError(FileTransfer::Error error, std::optional<std::string> response, const Args & ... args);
 
     virtual const char* sname() const override { return "FileTransferError"; }
 };
 
-bool isUri(const string & s);
+bool isUri(std::string_view s);
 
 /* Resolve deprecated 'channel:<foo>' URLs. */
-std::string resolveUri(const std::string & uri);
+std::string resolveUri(std::string_view uri);
 
 }

src/libstore/gc.cc

@@ -47,9 +47,8 @@ static void makeSymlink(const Path & link, const Path & target)
 
 void LocalStore::addIndirectRoot(const Path & path)
 {
-    string hash = hashString(htSHA1, path).to_string(Base32, false);
+    std::string hash = hashString(htSHA1, path).to_string(Base32, false);
-    Path realRoot = canonPath((format("%1%/%2%/auto/%3%")
+    Path realRoot = canonPath(fmt("%1%/%2%/auto/%3%", stateDir, gcRootsDir, hash));
-        % stateDir % gcRootsDir % hash).str());
     makeSymlink(realRoot, path);
 }
 
@@ -162,7 +161,7 @@ void LocalStore::addTempRoot(const StorePath & path)
     }
 
     /* Append the store path to the temporary roots file. */
-    string s = printStorePath(path) + '\0';
+    auto s = printStorePath(path) + '\0';
     writeFull(state->fdTempRoots.get(), s);
 }
 
@@ -203,12 +202,12 @@ void LocalStore::findTempRoots(Roots & tempRoots, bool censor)
         }
 
         /* Read the entire file. */
-        string contents = readFile(fd.get());
+        auto contents = readFile(fd.get());
 
         /* Extract the roots. */
-        string::size_type pos = 0, end;
+        std::string::size_type pos = 0, end;
 
-        while ((end = contents.find((char) 0, pos)) != string::npos) {
+        while ((end = contents.find((char) 0, pos)) != std::string::npos) {
             Path root(contents, pos, end - pos);
             debug("got temporary root '%s'", root);
             tempRoots[parseStorePath(root)].emplace(censor ? censored : fmt("{temp:%d}", pid));
@@ -305,7 +304,7 @@ Roots LocalStore::findRoots(bool censor)
 
 typedef std::unordered_map<Path, std::unordered_set<std::string>> UncheckedRoots;
 
-static void readProcLink(const string & file, UncheckedRoots & roots)
+static void readProcLink(const std::string & file, UncheckedRoots & roots)
 {
     /* 64 is the starting buffer size gnu readlink uses... */
     auto bufsiz = ssize_t{64};
@@ -328,7 +327,7 @@ try_again:
             .emplace(file);
 }
 
-static string quoteRegexChars(const string & raw)
+static std::string quoteRegexChars(const std::string & raw)
 {
     static auto specialRegex = std::regex(R"([.^$\\*+?()\[\]{}|])");
     return std::regex_replace(raw, specialRegex, R"(\$&)");
@@ -383,7 +382,7 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 
                 try {
                     auto mapFile = fmt("/proc/%s/maps", ent->d_name);
-                    auto mapLines = tokenizeString<std::vector<string>>(readFile(mapFile), "\n");
+                    auto mapLines = tokenizeString<std::vector<std::string>>(readFile(mapFile), "\n");
                     for (const auto & line : mapLines) {
                         auto match = std::smatch{};
                         if (std::regex_match(line, match, mapRegex))
@@ -784,7 +783,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
             struct dirent * dirent;
             while (errno = 0, dirent = readdir(dir.get())) {
                 checkInterrupt();
-                string name = dirent->d_name;
+                std::string name = dirent->d_name;
                 if (name == "." || name == ".." || name == linksName) continue;
 
                 if (auto storePath = maybeParseStorePath(storeDir + "/" + name))
@@ -825,7 +824,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
         struct dirent * dirent;
         while (errno = 0, dirent = readdir(dir.get())) {
             checkInterrupt();
-            string name = dirent->d_name;
+            std::string name = dirent->d_name;
             if (name == "." || name == "..") continue;
             Path path = linksDir + "/" + name;
 

src/libstore/globals.cc

@@ -100,7 +100,7 @@ std::vector<Path> getUserConfigFiles()
     // Use the paths specified in NIX_USER_CONF_FILES if it has been defined
     auto nixConfFiles = getEnv("NIX_USER_CONF_FILES");
     if (nixConfFiles.has_value()) {
-        return tokenizeString<std::vector<string>>(nixConfFiles.value(), ":");
+        return tokenizeString<std::vector<std::string>>(nixConfFiles.value(), ":");
     }
 
     // Use the paths specified by the XDG spec
@@ -181,7 +181,7 @@ bool Settings::isWSL1()
     return hasSuffix(utsbuf.release, "-Microsoft");
 }
 
-const string nixVersion = PACKAGE_VERSION;
+const std::string nixVersion = PACKAGE_VERSION;
 
 NLOHMANN_JSON_SERIALIZE_ENUM(SandboxMode, {
     {SandboxMode::smEnabled, true},

src/libstore/globals.hh

@@ -988,6 +988,6 @@ void loadConfFile();
 // Used by the Settings constructor
 std::vector<Path> getUserConfigFiles();
 
-extern const string nixVersion;
+extern const std::string nixVersion;
 
 }

src/libstore/legacy-ssh-store.cc

@@ -48,7 +48,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
 
     static std::set<std::string> uriSchemes() { return {"ssh"}; }
 
-    LegacySSHStore(const string & scheme, const string & host, const Params & params)
+    LegacySSHStore(const std::string & scheme, const std::string & host, const Params & params)
         : StoreConfig(params)
         , LegacySSHStoreConfig(params)
         , Store(params)
@@ -107,7 +107,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
         return conn;
     };
 
-    string getUri() override
+    std::string getUri() override
     {
         return *uriSchemes().begin() + "://" + host;
     }
@@ -225,13 +225,21 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
     std::optional<StorePath> queryPathFromHashPart(const std::string & hashPart) override
     { unsupported("queryPathFromHashPart"); }
 
-    StorePath addToStore(const string & name, const Path & srcPath,
+    StorePath addToStore(
-        FileIngestionMethod method, HashType hashAlgo,
+        std::string_view name,
-        PathFilter & filter, RepairFlag repair, const StorePathSet & references) override
+        const Path & srcPath,
+        FileIngestionMethod method,
+        HashType hashAlgo,
+        PathFilter & filter,
+        RepairFlag repair,
+        const StorePathSet & references) override
     { unsupported("addToStore"); }
 
-    StorePath addTextToStore(const string & name, const string & s,
+    StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair) override
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair) override
     { unsupported("addTextToStore"); }
 
 private:

src/libstore/local-fs-store.cc

@@ -85,7 +85,7 @@ void LocalFSStore::narFromPath(const StorePath & path, Sink & sink)
     dumpPath(getRealStoreDir() + std::string(printStorePath(path), storeDir.size()), sink);
 }
 
-const string LocalFSStore::drvsLogDir = "drvs";
+const std::string LocalFSStore::drvsLogDir = "drvs";
 
 std::optional<std::string> LocalFSStore::getBuildLog(const StorePath & path_)
 {

src/libstore/local-fs-store.hh

@@ -27,7 +27,7 @@ class LocalFSStore : public virtual LocalFSStoreConfig, public virtual Store
 {
 public:
 
-    const static string drvsLogDir;
+    const static std::string drvsLogDir;
 
     LocalFSStore(const Params & params);
 

src/libstore/local-store.cc

@@ -70,7 +70,7 @@ int getSchema(Path schemaPath)
 {
     int curSchema = 0;
     if (pathExists(schemaPath)) {
-        string s = readFile(schemaPath);
+        auto s = readFile(schemaPath);
         auto n = string2Int<int>(s);
         if (!n)
             throw Error("'%1%' is corrupt", schemaPath);
@@ -239,7 +239,7 @@ LocalStore::LocalStore(const Params & params)
             res = posix_fallocate(fd.get(), 0, settings.reservedSize);
 #endif
             if (res == -1) {
-                writeFull(fd.get(), string(settings.reservedSize, 'X'));
+                writeFull(fd.get(), std::string(settings.reservedSize, 'X'));
                 [[gnu::unused]] auto res2 = ftruncate(fd.get(), settings.reservedSize);
             }
         }
@@ -450,7 +450,7 @@ void LocalStore::openDB(State & state, bool create)
         throw SysError("Nix database directory '%1%' is not writable", dbDir);
 
     /* Open the Nix database. */
-    string dbPath = dbDir + "/db.sqlite";
+    std::string dbPath = dbDir + "/db.sqlite";
     auto & db(state.db);
     state.db = SQLite(dbPath, create);
 
@@ -471,19 +471,19 @@ void LocalStore::openDB(State & state, bool create)
        should be safe enough.  If the user asks for it, don't sync at
        all.  This can cause database corruption if the system
        crashes. */
-    string syncMode = settings.fsyncMetadata ? "normal" : "off";
+    std::string syncMode = settings.fsyncMetadata ? "normal" : "off";
     db.exec("pragma synchronous = " + syncMode);
 
     /* Set the SQLite journal mode.  WAL mode is fastest, so it's the
        default. */
-    string mode = settings.useSQLiteWAL ? "wal" : "truncate";
+    std::string mode = settings.useSQLiteWAL ? "wal" : "truncate";
-    string prevMode;
+    std::string prevMode;
     {
         SQLiteStmt stmt;
         stmt.create(db, "pragma main.journal_mode;");
         if (sqlite3_step(stmt) != SQLITE_ROW)
             throwSQLiteError(db, "querying journal mode");
-        prevMode = string((const char *) sqlite3_column_text(stmt, 0));
+        prevMode = std::string((const char *) sqlite3_column_text(stmt, 0));
     }
     if (prevMode != mode &&
         sqlite3_exec(db, ("pragma main.journal_mode = " + mode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
@@ -679,7 +679,7 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
 {
     assert(drvPath.isDerivation());
     std::string drvName(drvPath.name());
-    drvName = string(drvName, 0, drvName.size() - drvExtension.size());
+    drvName = drvName.substr(0, drvName.size() - drvExtension.size());
 
     auto envHasRightPath = [&](const StorePath & actual, const std::string & varName)
     {
@@ -786,7 +786,11 @@ void LocalStore::registerDrvOutput(const Realisation & info)
     });
 }
 
-void LocalStore::cacheDrvOutputMapping(State & state, const uint64_t deriver, const string & outputName, const StorePath & output)
+void LocalStore::cacheDrvOutputMapping(
+    State & state,
+    const uint64_t deriver,
+    const std::string & outputName,
+    const StorePath & output)
 {
     retrySQLite<void>([&]() {
         state.stmts->AddDerivationOutput.use()
@@ -795,7 +799,6 @@ void LocalStore::cacheDrvOutputMapping(State & state, const uint64_t deriver, co
             (printStorePath(output))
             .exec();
     });
-
 }
 
 
@@ -1436,7 +1439,9 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, std::string_view name
 }
 
 
-StorePath LocalStore::addTextToStore(const string & name, const string & s,
+StorePath LocalStore::addTextToStore(
+    std::string_view name,
+    std::string_view s,
     const StorePathSet & references, RepairFlag repair)
 {
     auto hash = hashString(htSHA256, s);
@@ -1548,7 +1553,7 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
         for (auto & link : readDirectory(linksDir)) {
             printMsg(lvlTalkative, "checking contents of '%s'", link.name);
             Path linkPath = linksDir + "/" + link.name;
-            string hash = hashPath(htSHA256, linkPath).first.to_string(Base32, false);
+            std::string hash = hashPath(htSHA256, linkPath).first.to_string(Base32, false);
             if (hash != link.name) {
                 printError("link '%s' was modified! expected hash '%s', got '%s'",
                     linkPath, link.name, hash);

src/libstore/local-store.hh

@@ -147,8 +147,11 @@ public:
     StorePath addToStoreFromDump(Source & dump, std::string_view name,
         FileIngestionMethod method, HashType hashAlgo, RepairFlag repair, const StorePathSet & references) override;
 
-    StorePath addTextToStore(const string & name, const string & s,
+    StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair) override;
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair) override;
 
     void addTempRoot(const StorePath & path) override;
 
@@ -204,7 +207,11 @@ public:
        derivation 'deriver'. */
     void registerDrvOutput(const Realisation & info) override;
     void registerDrvOutput(const Realisation & info, CheckSigsFlag checkSigs) override;
-    void cacheDrvOutputMapping(State & state, const uint64_t deriver, const string & outputName, const StorePath & output);
+    void cacheDrvOutputMapping(
+        State & state,
+        const uint64_t deriver,
+        const std::string & outputName,
+        const StorePath & output);
 
     std::optional<const Realisation> queryRealisation_(State & state, const DrvOutput & id);
     std::optional<std::pair<int64_t, Realisation>> queryRealisationCore_(State & state, const DrvOutput & id);

src/libstore/lock.hh

@@ -13,7 +13,7 @@ private:
     AutoCloseFD fdUserLock;
 
     bool isEnabled = false;
-    string user;
+    std::string user;
     uid_t uid = 0;
     gid_t gid = 0;
     std::vector<gid_t> supplementaryGIDs;
@@ -23,7 +23,7 @@ public:
 
     void kill();
 
-    string getUser() { return user; }
+    std::string getUser() { return user; }
     uid_t getUID() { assert(uid); return uid; }
     uid_t getGID() { assert(gid); return gid; }
     std::vector<gid_t> getSupplementaryGIDs() { return supplementaryGIDs; }

src/libstore/machines.cc

@@ -39,19 +39,19 @@ Machine::Machine(decltype(storeUri) storeUri,
     sshPublicHostKey(sshPublicHostKey)
 {}
 
-bool Machine::allSupported(const std::set<string> & features) const
+bool Machine::allSupported(const std::set<std::string> & features) const
 {
     return std::all_of(features.begin(), features.end(),
-        [&](const string & feature) {
+        [&](const std::string & feature) {
             return supportedFeatures.count(feature) ||
                 mandatoryFeatures.count(feature);
         });
 }
 
-bool Machine::mandatoryMet(const std::set<string> & features) const
+bool Machine::mandatoryMet(const std::set<std::string> & features) const
 {
     return std::all_of(mandatoryFeatures.begin(), mandatoryFeatures.end(),
-        [&](const string & feature) {
+        [&](const std::string & feature) {
             return features.count(feature);
         });
 }
@@ -89,7 +89,7 @@ ref<Store> Machine::openStore() const
 static std::vector<std::string> expandBuilderLines(const std::string & builders)
 {
     std::vector<std::string> result;
-    for (auto line : tokenizeString<std::vector<string>>(builders, "\n;")) {
+    for (auto line : tokenizeString<std::vector<std::string>>(builders, "\n;")) {
         trim(line);
         line.erase(std::find(line.begin(), line.end(), '#'), line.end());
         if (line.empty()) continue;
@@ -117,7 +117,7 @@ static std::vector<std::string> expandBuilderLines(const std::string & builders)
 
 static Machine parseBuilderLine(const std::string & line)
 {
-    const auto tokens = tokenizeString<std::vector<string>>(line);
+    const auto tokens = tokenizeString<std::vector<std::string>>(line);
 
     auto isSet = [&](size_t fieldIndex) {
         return tokens.size() > fieldIndex && tokens[fieldIndex] != "" && tokens[fieldIndex] != "-";
@@ -146,17 +146,18 @@ static Machine parseBuilderLine(const std::string & line)
 
     return {
         tokens[0],
-        isSet(1) ? tokenizeString<std::vector<string>>(tokens[1], ",") : std::vector<string>{settings.thisSystem},
+        isSet(1) ? tokenizeString<std::vector<std::string>>(tokens[1], ",") : std::vector<std::string>{settings.thisSystem},
         isSet(2) ? tokens[2] : "",
         isSet(3) ? parseUnsignedIntField(3) : 1U,
         isSet(4) ? parseUnsignedIntField(4) : 1U,
-        isSet(5) ? tokenizeString<std::set<string>>(tokens[5], ",") : std::set<string>{},
+        isSet(5) ? tokenizeString<std::set<std::string>>(tokens[5], ",") : std::set<std::string>{},
-        isSet(6) ? tokenizeString<std::set<string>>(tokens[6], ",") : std::set<string>{},
+        isSet(6) ? tokenizeString<std::set<std::string>>(tokens[6], ",") : std::set<std::string>{},
         isSet(7) ? ensureBase64(7) : ""
     };
 }
 
-static Machines parseBuilderLines(const std::vector<std::string>& builders) {
+static Machines parseBuilderLines(const std::vector<std::string> & builders)
+{
     Machines result;
     std::transform(builders.begin(), builders.end(), std::back_inserter(result), parseBuilderLine);
     return result;

src/libstore/nar-accessor.cc

@@ -90,7 +90,7 @@ struct NarAccessor : public FSAccessor
         void receiveContents(std::string_view data) override
         { }
 
-        void createSymlink(const Path & path, const string & target) override
+        void createSymlink(const Path & path, const std::string & target) override
         {
             createMember(path,
                 NarMember{FSAccessor::Type::tSymlink, false, 0, 0, target});

src/libstore/nar-info.cc

@@ -11,7 +11,7 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         return Error("NAR info file '%1%' is corrupt", whence);
     };
 
-    auto parseHashField = [&](const string & s) {
+    auto parseHashField = [&](const std::string & s) {
         try {
             return Hash::parseAnyPrefixed(s);
         } catch (BadHash &) {

src/libstore/optimise-store.cc

@@ -77,7 +77,7 @@ Strings LocalStore::readDirectoryIgnoringInodes(const Path & path, const InodeHa
             continue;
         }
 
-        string name = dirent->d_name;
+        std::string name = dirent->d_name;
         if (name == "." || name == "..") continue;
         names.push_back(name);
     }

src/libstore/path-with-outputs.cc

@@ -49,9 +49,9 @@ std::pair<std::string_view, StringSet> parsePathWithOutputs(std::string_view s)
 {
     size_t n = s.find("!");
     return n == s.npos
-        ? std::make_pair(s, std::set<string>())
+        ? std::make_pair(s, std::set<std::string>())
         : std::make_pair(((std::string_view) s).substr(0, n),
-            tokenizeString<std::set<string>>(((std::string_view) s).substr(n + 1), ","));
+            tokenizeString<std::set<std::string>>(((std::string_view) s).substr(n + 1), ","));
 }
 
 

src/libstore/path.hh

@@ -62,7 +62,7 @@ public:
 
 typedef std::set<StorePath> StorePathSet;
 typedef std::vector<StorePath> StorePaths;
-typedef std::map<string, StorePath> OutputPathMap;
+typedef std::map<std::string, StorePath> OutputPathMap;
 
 typedef std::map<StorePath, std::optional<ContentAddress>> StorePathCAMap;
 

src/libstore/pathlocks.cc

@@ -74,7 +74,7 @@ PathLocks::PathLocks()
 }
 
 
-PathLocks::PathLocks(const PathSet & paths, const string & waitMsg)
+PathLocks::PathLocks(const PathSet & paths, const std::string & waitMsg)
     : deletePaths(false)
 {
     lockPaths(paths, waitMsg);
@@ -82,7 +82,7 @@ PathLocks::PathLocks(const PathSet & paths, const string & waitMsg)
 
 
 bool PathLocks::lockPaths(const PathSet & paths,
-    const string & waitMsg, bool wait)
+    const std::string & waitMsg, bool wait)
 {
     assert(fds.empty());
 

src/libstore/pathlocks.hh

@@ -26,9 +26,9 @@ private:
 public:
     PathLocks();
     PathLocks(const PathSet & paths,
-        const string & waitMsg = "");
+        const std::string & waitMsg = "");
     bool lockPaths(const PathSet & _paths,
-        const string & waitMsg = "",
+        const std::string & waitMsg = "",
         bool wait = true);
     ~PathLocks();
     void unlock();

src/libstore/profiles.cc

@@ -15,12 +15,12 @@ namespace nix {
 
 /* Parse a generation name of the format
    `<profilename>-<number>-link'. */
-static std::optional<GenerationNumber> parseName(const string & profileName, const string & name)
+static std::optional<GenerationNumber> parseName(const std::string & profileName, const std::string & name)
 {
-    if (string(name, 0, profileName.size() + 1) != profileName + "-") return {};
+    if (name.substr(0, profileName.size() + 1) != profileName + "-") return {};
-    string s = string(name, profileName.size() + 1);
+    auto s = name.substr(profileName.size() + 1);
-    string::size_type p = s.find("-link");
+    auto p = s.find("-link");
-    if (p == string::npos) return {};
+    if (p == std::string::npos) return {};
     if (auto n = string2Int<unsigned int>(s.substr(0, p)))
         return *n;
     else
@@ -209,13 +209,13 @@ void deleteGenerationsOlderThan(const Path & profile, time_t t, bool dryRun)
 }
 
 
-void deleteGenerationsOlderThan(const Path & profile, const string & timeSpec, bool dryRun)
+void deleteGenerationsOlderThan(const Path & profile, std::string_view timeSpec, bool dryRun)
 {
     if (timeSpec.empty() || timeSpec[timeSpec.size() - 1] != 'd')
         throw UsageError("invalid number of days specifier '%1%', expected something like '14d'", timeSpec);
 
     time_t curTime = time(0);
-    string strDays = string(timeSpec, 0, timeSpec.size() - 1);
+    auto strDays = timeSpec.substr(0, timeSpec.size() - 1);
     auto days = string2Int<int>(strDays);
 
     if (!days || *days < 1)
@@ -274,7 +274,7 @@ void lockProfile(PathLocks & lock, const Path & profile)
 }
 
 
-string optimisticLockProfile(const Path & profile)
+std::string optimisticLockProfile(const Path & profile)
 {
     return pathExists(profile) ? readLink(profile) : "";
 }

src/libstore/profiles.hh

@@ -42,7 +42,7 @@ void deleteOldGenerations(const Path & profile, bool dryRun);
 
 void deleteGenerationsOlderThan(const Path & profile, time_t t, bool dryRun);
 
-void deleteGenerationsOlderThan(const Path & profile, const string & timeSpec, bool dryRun);
+void deleteGenerationsOlderThan(const Path & profile, std::string_view timeSpec, bool dryRun);
 
 void switchLink(Path link, Path target);
 
@@ -66,7 +66,7 @@ void lockProfile(PathLocks & lock, const Path & profile);
    generally cheap, since the build results are still in the Nix
    store.  Most of the time, only the user environment has to be
    rebuilt. */
-string optimisticLockProfile(const Path & profile);
+std::string optimisticLockProfile(const Path & profile);
 
 /* Resolve ~/.nix-profile. If ~/.nix-profile doesn't exist yet, create
    it. */

src/libstore/references.cc

@@ -68,7 +68,7 @@ void RefScanSink::operator () (std::string_view data)
 
 
 std::pair<StorePathSet, HashResult> scanForReferences(
-    const string & path,
+    const std::string & path,
     const StorePathSet & refs)
 {
     HashSink hashSink { htSHA256 };
@@ -121,7 +121,7 @@ void RewritingSink::operator () (std::string_view data)
     s.append(data);
 
     size_t j = 0;
-    while ((j = s.find(from, j)) != string::npos) {
+    while ((j = s.find(from, j)) != std::string::npos) {
         matches.push_back(pos + j);
         s.replace(j, from.size(), to);
     }

src/libstore/remote-store.cc

@@ -661,8 +661,11 @@ void RemoteStore::addMultipleToStore(
 }
 
 
-StorePath RemoteStore::addTextToStore(const string & name, const string & s,
+StorePath RemoteStore::addTextToStore(
-    const StorePathSet & references, RepairFlag repair)
+    std::string_view name,
+    std::string_view s,
+    const StorePathSet & references,
+    RepairFlag repair)
 {
     StringSource source(s);
     return addCAToStore(source, name, TextHashMethod{}, references, repair)->path;
@@ -1000,7 +1003,7 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
         auto msg = readNum<uint64_t>(from);
 
         if (msg == STDERR_WRITE) {
-            string s = readString(from);
+            auto s = readString(from);
             if (!sink) throw Error("no sink");
             (*sink)(s);
         }
@@ -1017,7 +1020,7 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
             if (GET_PROTOCOL_MINOR(daemonVersion) >= 26) {
                 return std::make_exception_ptr(readError(from));
             } else {
-                string error = readString(from);
+                auto error = readString(from);
                 unsigned int status = readInt(from);
                 return std::make_exception_ptr(Error(status, error));
             }

src/libstore/remote-store.hh

@@ -83,8 +83,11 @@ public:
         RepairFlag repair,
         CheckSigsFlag checkSigs) override;
 
-    StorePath addTextToStore(const string & name, const string & s,
+    StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair) override;
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair) override;
 
     void registerDrvOutput(const Realisation & info) override;
 

src/libstore/s3-binary-cache-store.cc

@@ -87,7 +87,11 @@ static void initAWS()
     });
 }
 
-S3Helper::S3Helper(const string & profile, const string & region, const string & scheme, const string & endpoint)
+S3Helper::S3Helper(
+    const std::string & profile,
+    const std::string & region,
+    const std::string & scheme,
+    const std::string & endpoint)
     : config(makeConfig(region, scheme, endpoint))
     , client(make_ref<Aws::S3::S3Client>(
             profile == ""
@@ -121,7 +125,10 @@ class RetryStrategy : public Aws::Client::DefaultRetryStrategy
     }
 };
 
-ref<Aws::Client::ClientConfiguration> S3Helper::makeConfig(const string & region, const string & scheme, const string & endpoint)
+ref<Aws::Client::ClientConfiguration> S3Helper::makeConfig(
+    const std::string & region,
+    const std::string & scheme,
+    const std::string & endpoint)
 {
     initAWS();
     auto res = make_ref<Aws::Client::ClientConfiguration>();

src/libstore/sqlite.cc

@@ -71,7 +71,7 @@ uint64_t SQLite::getLastInsertedRowId()
     return sqlite3_last_insert_rowid(db);
 }
 
-void SQLiteStmt::create(sqlite3 * db, const string & sql)
+void SQLiteStmt::create(sqlite3 * db, const std::string & sql)
 {
     checkInterrupt();
     assert(!stmt);

src/libstore/ssh.cc

@@ -29,7 +29,7 @@ void SSHMaster::addCommonSSHOpts(Strings & args)
     if (!sshPublicHostKey.empty()) {
         Path fileName = (Path) *state->tmpDir + "/host-key";
         auto p = host.rfind("@");
-        string thost = p != string::npos ? string(host, p + 1) : host;
+        std::string thost = p != std::string::npos ? std::string(host, p + 1) : host;
         writeFile(fileName, thost + " " + base64Decode(sshPublicHostKey) + "\n");
         args.insert(args.end(), {"-oUserKnownHostsFile=" + fileName});
     }

src/libstore/store-api.cc

@@ -39,7 +39,7 @@ Path Store::followLinksToStore(std::string_view _path) const
     Path path = absPath(std::string(_path));
     while (!isInStore(path)) {
         if (!isLink(path)) break;
-        string target = readLink(path);
+        auto target = readLink(path);
         path = absPath(target, dirOf(path));
     }
     if (!isInStore(path))
@@ -138,8 +138,8 @@ StorePath Store::makeStorePath(std::string_view type,
     std::string_view hash, std::string_view name) const
 {
     /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
-    string s = std::string { type } + ":" + std::string { hash }
+    auto s = std::string(type) + ":" + std::string(hash)
-        + ":" + storeDir + ":" + std::string { name };
+        + ":" + storeDir + ":" + std::string(name);
     auto h = compressHash(hashString(htSHA256, s), 20);
     return StorePath(h, name);
 }
@@ -161,7 +161,7 @@ StorePath Store::makeOutputPath(std::string_view id,
 
 static std::string makeType(
     const Store & store,
-    string && type,
+    std::string && type,
     const StorePathSet & references,
     bool hasSelfReference = false)
 {
@@ -229,15 +229,23 @@ std::pair<StorePath, Hash> Store::computeStorePathForPath(std::string_view name,
 }
 
 
-StorePath Store::computeStorePathForText(const string & name, const string & s,
+StorePath Store::computeStorePathForText(
+    std::string_view name,
+    std::string_view s,
     const StorePathSet & references) const
 {
     return makeTextPath(name, hashString(htSHA256, s), references);
 }
 
 
-StorePath Store::addToStore(const string & name, const Path & _srcPath,
+StorePath Store::addToStore(
-    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair, const StorePathSet & references)
+    std::string_view name,
+    const Path & _srcPath,
+    FileIngestionMethod method,
+    HashType hashAlgo,
+    PathFilter & filter,
+    RepairFlag repair,
+    const StorePathSet & references)
 {
     Path srcPath(absPath(_srcPath));
     auto source = sinkToSource([&](Sink & sink) {
@@ -688,10 +696,10 @@ StorePathSet Store::queryValidPaths(const StorePathSet & paths, SubstituteFlag m
 /* Return a string accepted by decodeValidPathInfo() that
    registers the specified paths as valid.  Note: it's the
    responsibility of the caller to provide a closure. */
-string Store::makeValidityRegistration(const StorePathSet & paths,
+std::string Store::makeValidityRegistration(const StorePathSet & paths,
     bool showDerivers, bool showHash)
 {
-    string s = "";
+    std::string s = "";
 
     for (auto & i : paths) {
         s += printStorePath(i) + "\n";
@@ -1131,7 +1139,7 @@ std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istre
     getline(str, path);
     if (str.eof()) { return {}; }
     if (!hashGiven) {
-        string s;
+        std::string s;
         getline(str, s);
         auto narHash = Hash::parseAny(s, htSHA256);
         getline(str, s);
@@ -1144,7 +1152,7 @@ std::optional<ValidPathInfo> decodeValidPathInfo(const Store & store, std::istre
     std::string deriver;
     getline(str, deriver);
     if (deriver != "") info.deriver = store.parseStorePath(deriver);
-    string s;
+    std::string s;
     getline(str, s);
     auto n = string2Int<int>(s);
     if (!n) throw Error("number expected");
@@ -1168,7 +1176,7 @@ std::string Store::showPaths(const StorePathSet & paths)
 }
 
 
-string showPaths(const PathSet & paths)
+std::string showPaths(const PathSet & paths)
 {
     return concatStringsSep(", ", quoteStrings(paths));
 }

src/libstore/store-api.hh

@@ -352,7 +352,9 @@ public:
        simply yield a different store path, so other users wouldn't be
        affected), but it has some backwards compatibility issues (the
        hashing scheme changes), so I'm not doing that for now. */
-    StorePath computeStorePathForText(const string & name, const string & s,
+    StorePath computeStorePathForText(
+        std::string_view name,
+        std::string_view s,
         const StorePathSet & references) const;
 
     /* Check whether a path is valid. */
@@ -482,9 +484,14 @@ public:
        validity the resulting path.  The resulting path is returned.
        The function object `filter' can be used to exclude files (see
        libutil/archive.hh). */
-    virtual StorePath addToStore(const string & name, const Path & srcPath,
+    virtual StorePath addToStore(
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
+        std::string_view name,
-        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair, const StorePathSet & references = StorePathSet());
+        const Path & srcPath,
+        FileIngestionMethod method = FileIngestionMethod::Recursive,
+        HashType hashAlgo = htSHA256,
+        PathFilter & filter = defaultPathFilter,
+        RepairFlag repair = NoRepair,
+        const StorePathSet & references = StorePathSet());
 
     /* Copy the contents of a path to the store and register the
        validity the resulting path, using a constant amount of
@@ -506,8 +513,11 @@ public:
 
     /* Like addToStore, but the contents written to the output path is
        a regular file containing the given string. */
-    virtual StorePath addTextToStore(const string & name, const string & s,
+    virtual StorePath addTextToStore(
-        const StorePathSet & references, RepairFlag repair = NoRepair) = 0;
+        std::string_view name,
+        std::string_view s,
+        const StorePathSet & references,
+        RepairFlag repair = NoRepair) = 0;
 
     /**
      * Add a mapping indicating that `deriver!outputName` maps to the output path
@@ -608,7 +618,7 @@ public:
     /* Return a string representing information about the path that
        can be loaded into the database using `nix-store --load-db' or
        `nix-store --register-validity'. */
-    string makeValidityRegistration(const StorePathSet & paths,
+    std::string makeValidityRegistration(const StorePathSet & paths,
         bool showDerivers, bool showHash);
 
     /* Write a JSON representation of store path metadata, such as the
@@ -910,7 +920,7 @@ struct RegisterStoreImplementation
 
 /* Display a set of paths in human-readable form (i.e., between quotes
    and separated by commas). */
-string showPaths(const PathSet & paths);
+std::string showPaths(const PathSet & paths);
 
 
 std::optional<ValidPathInfo> decodeValidPathInfo(

src/libutil/archive.cc

@@ -37,7 +37,7 @@ static GlobalConfig::Register rArchiveSettings(&archiveSettings);
 
 const std::string narVersionMagic1 = "nix-archive-1";
 
-static string caseHackSuffix = "~nix~case~hack~";
+static std::string caseHackSuffix = "~nix~case~hack~";
 
 PathFilter defaultPathFilter = [](const Path &) { return true; };
 
@@ -84,12 +84,12 @@ static void dump(const Path & path, Sink & sink, PathFilter & filter)
 
         /* If we're on a case-insensitive system like macOS, undo
            the case hack applied by restorePath(). */
-        std::map<string, string> unhacked;
+        std::map<std::string, std::string> unhacked;
         for (auto & i : readDirectory(path))
             if (archiveSettings.useCaseHack) {
-                string name(i.name);
+                std::string name(i.name);
                 size_t pos = i.name.find(caseHackSuffix);
-                if (pos != string::npos) {
+                if (pos != std::string::npos) {
                     debug(format("removing case hack suffix from '%1%'") % (path + "/" + i.name));
                     name.erase(pos);
                 }
@@ -124,13 +124,13 @@ void dumpPath(const Path & path, Sink & sink, PathFilter & filter)
 }
 
 
-void dumpString(const std::string & s, Sink & sink)
+void dumpString(std::string_view s, Sink & sink)
 {
     sink << narVersionMagic1 << "(" << "type" << "regular" << "contents" << s << ")";
 }
 
 
-static SerialisationError badArchive(string s)
+static SerialisationError badArchive(const std::string & s)
 {
     return SerialisationError("bad archive: " + s);
 }
@@ -171,7 +171,7 @@ static void parseContents(ParseSink & sink, Source & source, const Path & path)
 
 struct CaseInsensitiveCompare
 {
-    bool operator() (const string & a, const string & b) const
+    bool operator() (const std::string & a, const std::string & b) const
     {
         return strcasecmp(a.c_str(), b.c_str()) < 0;
     }
@@ -180,7 +180,7 @@ struct CaseInsensitiveCompare
 
 static void parse(ParseSink & sink, Source & source, const Path & path)
 {
-    string s;
+    std::string s;
 
     s = readString(source);
     if (s != "(") throw badArchive("expected open tag");
@@ -201,7 +201,7 @@ static void parse(ParseSink & sink, Source & source, const Path & path)
         else if (s == "type") {
             if (type != tpUnknown)
                 throw badArchive("multiple type fields");
-            string t = readString(source);
+            std::string t = readString(source);
 
             if (t == "regular") {
                 type = tpRegular;
@@ -232,7 +232,7 @@ static void parse(ParseSink & sink, Source & source, const Path & path)
         }
 
         else if (s == "entry" && type == tpDirectory) {
-            string name, prevName;
+            std::string name, prevName;
 
             s = readString(source);
             if (s != "(") throw badArchive("expected open tag");
@@ -246,7 +246,7 @@ static void parse(ParseSink & sink, Source & source, const Path & path)
                     break;
                 } else if (s == "name") {
                     name = readString(source);
-                    if (name.empty() || name == "." || name == ".." || name.find('/') != string::npos || name.find((char) 0) != string::npos)
+                    if (name.empty() || name == "." || name == ".." || name.find('/') != std::string::npos || name.find((char) 0) != std::string::npos)
                         throw Error("NAR contains invalid file name '%1%'", name);
                     if (name <= prevName)
                         throw Error("NAR directory is not sorted");
@@ -269,7 +269,7 @@ static void parse(ParseSink & sink, Source & source, const Path & path)
         }
 
         else if (s == "target" && type == tpSymlink) {
-            string target = readString(source);
+            std::string target = readString(source);
             sink.createSymlink(path, target);
         }
 
@@ -281,7 +281,7 @@ static void parse(ParseSink & sink, Source & source, const Path & path)
 
 void parseDump(ParseSink & sink, Source & source)
 {
-    string version;
+    std::string version;
     try {
         version = readString(source, narVersionMagic1.size());
     } catch (SerialisationError & e) {
@@ -345,7 +345,7 @@ struct RestoreSink : ParseSink
         writeFull(fd.get(), data);
     }
 
-    void createSymlink(const Path & path, const string & target) override
+    void createSymlink(const Path & path, const std::string & target) override
     {
         Path p = dstPath + path;
         nix::createSymlink(target, p);

src/libutil/archive.hh

@@ -48,7 +48,7 @@ namespace nix {
 void dumpPath(const Path & path, Sink & sink,
     PathFilter & filter = defaultPathFilter);
 
-void dumpString(const std::string & s, Sink & sink);
+void dumpString(std::string_view s, Sink & sink);
 
 /* FIXME: fix this API, it sucks. */
 struct ParseSink
@@ -60,7 +60,7 @@ struct ParseSink
     virtual void preallocateContents(uint64_t size) { };
     virtual void receiveContents(std::string_view data) { };
 
-    virtual void createSymlink(const Path & path, const string & target) { };
+    virtual void createSymlink(const Path & path, const std::string & target) { };
 };
 
 /* If the NAR archive contains a single file at top-level, then save
@@ -82,7 +82,7 @@ struct RetrieveRegularNARSink : ParseSink
         sink(data);
     }
 
-    void createSymlink(const Path & path, const string & target) override
+    void createSymlink(const Path & path, const std::string & target) override
     {
         regular = false;
     }

src/libutil/args.cc

@@ -76,13 +76,13 @@ void Args::parseCmdline(const Strings & _cmdline)
         /* Expand compound dash options (i.e., `-qlf' -> `-q -l -f',
            `-j3` -> `-j 3`). */
         if (!dashDash && arg.length() > 2 && arg[0] == '-' && arg[1] != '-' && isalpha(arg[1])) {
-            *pos = (string) "-" + arg[1];
+            *pos = (std::string) "-" + arg[1];
             auto next = pos; ++next;
             for (unsigned int j = 2; j < arg.length(); j++)
                 if (isalpha(arg[j]))
-                    cmdline.insert(next, (string) "-" + arg[j]);
+                    cmdline.insert(next, (std::string) "-" + arg[j]);
                 else {
-                    cmdline.insert(next, string(arg, j));
+                    cmdline.insert(next, std::string(arg, j));
                     break;
                 }
             arg = *pos;
@@ -139,7 +139,7 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
         return true;
     };
 
-    if (string(*pos, 0, 2) == "--") {
+    if (std::string(*pos, 0, 2) == "--") {
         if (auto prefix = needsCompletion(*pos)) {
             for (auto & [name, flag] : longFlags) {
                 if (!hiddenCategories.count(flag->category)
@@ -147,12 +147,12 @@ bool Args::processFlag(Strings::iterator & pos, Strings::iterator end)
                     completions->add("--" + name, flag->description);
             }
         }
-        auto i = longFlags.find(string(*pos, 2));
+        auto i = longFlags.find(std::string(*pos, 2));
         if (i == longFlags.end()) return false;
         return process("--" + i->first, *i->second);
     }
 
-    if (string(*pos, 0, 1) == "-" && pos->size() == 2) {
+    if (std::string(*pos, 0, 1) == "-" && pos->size() == 2) {
         auto c = (*pos)[1];
         auto i = shortFlags.find(c);
         if (i == shortFlags.end()) return false;

src/libutil/args.hh

@@ -158,7 +158,7 @@ public:
     }
 
     /* Expect a string argument. */
-    void expectArg(const std::string & label, string * dest, bool optional = false)
+    void expectArg(const std::string & label, std::string * dest, bool optional = false)
     {
         expectArgs({
             .label = label,

src/libutil/config.cc

@@ -81,16 +81,16 @@ void AbstractConfig::applyConfig(const std::string & contents, const std::string
     unsigned int pos = 0;
 
     while (pos < contents.size()) {
-        string line;
+        std::string line;
         while (pos < contents.size() && contents[pos] != '\n')
             line += contents[pos++];
         pos++;
 
-        string::size_type hash = line.find('#');
+        auto hash = line.find('#');
-        if (hash != string::npos)
+        if (hash != std::string::npos)
-            line = string(line, 0, hash);
+            line = std::string(line, 0, hash);
 
-        auto tokens = tokenizeString<std::vector<string>>(line);
+        auto tokens = tokenizeString<std::vector<std::string>>(line);
         if (tokens.empty()) continue;
 
         if (tokens.size() < 2)
@@ -120,7 +120,7 @@ void AbstractConfig::applyConfig(const std::string & contents, const std::string
         if (tokens[1] != "=")
             throw UsageError("illegal configuration line '%1%' in '%2%'", line, path);
 
-        string name = tokens[0];
+        std::string name = tokens[0];
 
         auto i = tokens.begin();
         advance(i, 2);
@@ -132,7 +132,7 @@ void AbstractConfig::applyConfig(const std::string & contents, const std::string
 void AbstractConfig::applyConfigFile(const Path & path)
 {
     try {
-        string contents = readFile(path);
+        std::string contents = readFile(path);
         applyConfig(contents, path);
     } catch (SysError &) { }
 }

src/libutil/error.cc

@@ -17,7 +17,7 @@ BaseError & BaseError::addTrace(std::optional<ErrPos> e, hintformat hint)
 
 // c++ std::exception descendants must have a 'const char* what()' function.
 // This stringifies the error and caches it for use by what(), or similarly by msg().
-const string & BaseError::calcWhat() const
+const std::string & BaseError::calcWhat() const
 {
     if (what_.has_value())
         return *what_;
@@ -32,14 +32,14 @@ const string & BaseError::calcWhat() const
     }
 }
 
-std::optional<string> ErrorInfo::programName = std::nullopt;
+std::optional<std::string> ErrorInfo::programName = std::nullopt;
 
 std::ostream & operator<<(std::ostream & os, const hintformat & hf)
 {
     return os << hf.str();
 }
 
-string showErrPos(const ErrPos & errPos)
+std::string showErrPos(const ErrPos & errPos)
 {
     if (errPos.line > 0) {
         if (errPos.column > 0) {
@@ -68,7 +68,7 @@ std::optional<LinesOfCode> getCodeLines(const ErrPos & errPos)
 
             // count the newlines.
             int count = 0;
-            string line;
+            std::string line;
             int pl = errPos.line - 1;
             do
             {
@@ -100,7 +100,7 @@ std::optional<LinesOfCode> getCodeLines(const ErrPos & errPos)
         std::istringstream iss(errPos.file);
         // count the newlines.
         int count = 0;
-        string line;
+        std::string line;
         int pl = errPos.line - 1;
 
         LinesOfCode loc;
@@ -132,7 +132,7 @@ std::optional<LinesOfCode> getCodeLines(const ErrPos & errPos)
 
 // print lines of code to the ostream, indicating the error column.
 void printCodeLines(std::ostream & out,
-    const string & prefix,
+    const std::string & prefix,
     const ErrPos & errPos,
     const LinesOfCode & loc)
 {

src/libutil/error.hh

@@ -61,16 +61,16 @@ typedef enum {
 
 // the lines of code surrounding an error.
 struct LinesOfCode {
-    std::optional<string> prevLineOfCode;
+    std::optional<std::string> prevLineOfCode;
-    std::optional<string> errLineOfCode;
+    std::optional<std::string> errLineOfCode;
-    std::optional<string> nextLineOfCode;
+    std::optional<std::string> nextLineOfCode;
 };
 
 // ErrPos indicates the location of an error in a nix file.
 struct ErrPos {
     int line = 0;
     int column = 0;
-    string file;
+    std::string file;
     FileOrigin origin;
 
     operator bool() const
@@ -107,12 +107,12 @@ struct Trace {
 
 struct ErrorInfo {
     Verbosity level;
-    string name; // FIXME: rename
+    std::string name; // FIXME: rename
     hintformat msg;
     std::optional<ErrPos> errPos;
     std::list<Trace> traces;
 
-    static std::optional<string> programName;
+    static std::optional<std::string> programName;
 };
 
 std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool showTrace);
@@ -124,8 +124,8 @@ class BaseError : public std::exception
 protected:
     mutable ErrorInfo err;
 
-    mutable std::optional<string> what_;
+    mutable std::optional<std::string> what_;
-    const string& calcWhat() const;
+    const std::string & calcWhat() const;
 
 public:
     unsigned int status = 1; // exit status
@@ -162,11 +162,11 @@ public:
     const char * what() const noexcept override { return calcWhat().c_str(); }
 #endif
 
-    const string & msg() const { return calcWhat(); }
+    const std::string & msg() const { return calcWhat(); }
     const ErrorInfo & info() const { calcWhat(); return err; }
 
     template<typename... Args>
-    BaseError & addTrace(std::optional<ErrPos> e, const string &fs, const Args & ... args)
+    BaseError & addTrace(std::optional<ErrPos> e, const std::string & fs, const Args & ... args)
     {
         return addTrace(e, hintfmt(fs, args...));
     }

src/libutil/fmt.hh

@@ -10,7 +10,6 @@ namespace nix {
 
 
 /* Inherit some names from other namespaces for convenience. */
-using std::string;
 using boost::format;
 
 
@@ -21,8 +20,8 @@ struct nop { template<typename... T> nop(T...) {} };
 
 struct FormatOrString
 {
-    string s;
+    std::string s;
-    FormatOrString(const string & s) : s(s) { };
+    FormatOrString(std::string s) : s(std::move(s)) { };
     template<class F>
     FormatOrString(const F & f) : s(f.str()) { };
     FormatOrString(const char * s) : s(s) { };
@@ -102,7 +101,7 @@ std::ostream & operator<<(std::ostream & out, const normaltxt<T> & y)
 class hintformat
 {
 public:
-    hintformat(const string & format) : fmt(format)
+    hintformat(const std::string & format) : fmt(format)
     {
         fmt.exceptions(boost::io::all_error_bits ^
                        boost::io::too_many_args_bit ^

src/libutil/hash.cc

@@ -66,31 +66,31 @@ bool Hash::operator < (const Hash & h) const
 }
 
 
-const string base16Chars = "0123456789abcdef";
+const std::string base16Chars = "0123456789abcdef";
 
 
-static string printHash16(const Hash & hash)
+static std::string printHash16(const Hash & hash)
 {
     char buf[hash.hashSize * 2];
     for (unsigned int i = 0; i < hash.hashSize; i++) {
         buf[i * 2] = base16Chars[hash.hash[i] >> 4];
         buf[i * 2 + 1] = base16Chars[hash.hash[i] & 0x0f];
     }
-    return string(buf, hash.hashSize * 2);
+    return std::string(buf, hash.hashSize * 2);
 }
 
 
 // omitted: E O U T
-const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
+const std::string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
 
 
-static string printHash32(const Hash & hash)
+static std::string printHash32(const Hash & hash)
 {
     assert(hash.hashSize);
     size_t len = hash.base32Len();
     assert(len);
 
-    string s;
+    std::string s;
     s.reserve(len);
 
     for (int n = (int) len - 1; n >= 0; n--) {
@@ -107,7 +107,7 @@ static string printHash32(const Hash & hash)
 }
 
 
-string printHash16or32(const Hash & hash)
+std::string printHash16or32(const Hash & hash)
 {
     assert(hash.type);
     return hash.to_string(hash.type == htMD5 ? Base16 : Base32, false);
@@ -151,7 +151,8 @@ Hash Hash::parseSRI(std::string_view original) {
 }
 
 // Mutates the string to eliminate the prefixes when found
-static std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_view & rest) {
+static std::pair<std::optional<HashType>, bool> getParsedTypeAndSRI(std::string_view & rest)
+{
     bool isSRI = false;
 
     // Parse the has type before the separater, if there was one.
@@ -402,7 +403,7 @@ HashType parseHashType(std::string_view s)
         throw UsageError("unknown hash algorithm '%1%'", s);
 }
 
-string printHashType(HashType ht)
+std::string printHashType(HashType ht)
 {
     switch (ht) {
     case htMD5: return "md5";

src/libutil/hash.hh

@@ -20,7 +20,7 @@ const int sha512HashSize = 64;
 
 extern std::set<std::string> hashTypes;
 
-extern const string base32Chars;
+extern const std::string base32Chars;
 
 enum Base : int { Base64, Base32, Base16, SRI };
 
@@ -110,7 +110,7 @@ public:
 Hash newHashAllowEmpty(std::string_view hashStr, std::optional<HashType> ht);
 
 /* Print a hash in base-16 if it's MD5, or base-32 otherwise. */
-string printHash16or32(const Hash & hash);
+std::string printHash16or32(const Hash & hash);
 
 /* Compute the hash of the given string. */
 Hash hashString(HashType ht, std::string_view s);
@@ -135,7 +135,7 @@ HashType parseHashType(std::string_view s);
 std::optional<HashType> parseHashTypeOpt(std::string_view s);
 
 /* And the reverse. */
-string printHashType(HashType ht);
+std::string printHashType(HashType ht);
 
 
 union Ctx;

src/libutil/logging.cc

@@ -113,7 +113,7 @@ void warnOnce(bool & haveWarned, const FormatOrString & fs)
     }
 }
 
-void writeToStderr(const string & s)
+void writeToStderr(std::string_view s)
 {
     try {
         writeFull(STDERR_FILENO, s, false);

src/libutil/logging.hh

@@ -216,6 +216,6 @@ inline void warn(const std::string & fs, const Args & ... args)
 
 void warnOnce(bool & haveWarned, const FormatOrString & fs);
 
-void writeToStderr(const string & s);
+void writeToStderr(std::string_view s);
 
 }

src/libutil/serialise.cc

@@ -391,7 +391,7 @@ size_t readString(char * buf, size_t max, Source & source)
 }
 
 
-string readString(Source & source, size_t max)
+std::string readString(Source & source, size_t max)
 {
     auto len = readNum<size_t>(source);
     if (len > max) throw SerialisationError("string is too long");
@@ -401,7 +401,7 @@ string readString(Source & source, size_t max)
     return res;
 }
 
-Source & operator >> (Source & in, string & s)
+Source & operator >> (Source & in, std::string & s)
 {
     s = readString(in);
     return in;

src/libutil/serialise.hh

@@ -364,10 +364,10 @@ inline uint64_t readLongLong(Source & source)
 
 void readPadding(size_t len, Source & source);
 size_t readString(char * buf, size_t max, Source & source);
-string readString(Source & source, size_t max = std::numeric_limits<size_t>::max());
+std::string readString(Source & source, size_t max = std::numeric_limits<size_t>::max());
 template<class T> T readStrings(Source & source);
 
-Source & operator >> (Source & in, string & s);
+Source & operator >> (Source & in, std::string & s);
 
 template<typename T>
 Source & operator >> (Source & in, T & n)

src/libutil/tests/url.cc

@@ -5,9 +5,9 @@ namespace nix {
 
 /* ----------- tests for url.hh --------------------------------------------------*/
 
-    string print_map(std::map<string, string> m) {
+    std::string print_map(std::map<std::string, std::string> m) {
-        std::map<string, string>::iterator it;
+        std::map<std::string, std::string>::iterator it;
-        string s = "{ ";
+        std::string s = "{ ";
         for (it = m.begin(); it != m.end(); ++it) {
             s += "{ ";
             s += it->first;
@@ -262,21 +262,21 @@ namespace nix {
      * --------------------------------------------------------------------------*/
 
     TEST(percentDecode, decodesUrlEncodedString) {
-        string s = "==@==";
+        std::string s = "==@==";
-        string d = percentDecode("%3D%3D%40%3D%3D");
+        std::string d = percentDecode("%3D%3D%40%3D%3D");
         ASSERT_EQ(d, s);
     }
 
     TEST(percentDecode, multipleDecodesAreIdempotent) {
-        string once = percentDecode("%3D%3D%40%3D%3D");
+        std::string once = percentDecode("%3D%3D%40%3D%3D");
-        string twice = percentDecode(once);
+        std::string twice = percentDecode(once);
 
         ASSERT_EQ(once, twice);
     }
 
     TEST(percentDecode, trailingPercent) {
-        string s = "==@==%";
+        std::string s = "==@==%";
-        string d = percentDecode("%3D%3D%40%3D%3D%25");
+        std::string d = percentDecode("%3D%3D%40%3D%3D%25");
 
         ASSERT_EQ(d, s);
     }

src/libutil/types.hh

@@ -14,6 +14,7 @@ namespace nix {
 typedef std::list<std::string> Strings;
 typedef std::set<std::string> StringSet;
 typedef std::map<std::string, std::string> StringMap;
+typedef std::map<std::string, std::string> StringPairs;
 
 /* Paths are just strings. */
 typedef std::string Path;

src/libutil/util.cc

@@ -110,13 +110,13 @@ Path canonPath(PathView path, bool resolveSymlinks)
 {
     assert(path != "");
 
-    string s;
+    std::string s;
     s.reserve(256);
 
     if (path[0] != '/')
         throw Error("not an absolute path: '%1%'", path);
 
-    string temp;
+    std::string temp;
 
     /* Count the number of times we follow a symlink and stop at some
        arbitrary (but high) limit to prevent infinite loops. */
@@ -142,7 +142,7 @@ Path canonPath(PathView path, bool resolveSymlinks)
         /* Normal component; copy it. */
         else {
             s += '/';
-            if (const auto slash = path.find('/'); slash == string::npos) {
+            if (const auto slash = path.find('/'); slash == std::string::npos) {
                 s += path;
                 path = {};
             } else {
@@ -175,7 +175,7 @@ Path canonPath(PathView path, bool resolveSymlinks)
 Path dirOf(const PathView path)
 {
     Path::size_type pos = path.rfind('/');
-    if (pos == string::npos)
+    if (pos == std::string::npos)
         return ".";
     return pos == 0 ? "/" : Path(path, 0, pos);
 }
@@ -191,7 +191,7 @@ std::string_view baseNameOf(std::string_view path)
         last -= 1;
 
     auto pos = path.rfind('/', last);
-    if (pos == string::npos)
+    if (pos == std::string::npos)
         pos = 0;
     else
         pos += 1;
@@ -249,7 +249,7 @@ Path readLink(const Path & path)
             else
                 throw SysError("reading symbolic link '%1%'", path);
         else if (rlSize < bufSize)
-            return string(buf.data(), rlSize);
+            return std::string(buf.data(), rlSize);
     }
 }
 
@@ -269,7 +269,7 @@ DirEntries readDirectory(DIR *dir, const Path & path)
     struct dirent * dirent;
     while (errno = 0, dirent = readdir(dir)) { /* sic */
         checkInterrupt();
-        string name = dirent->d_name;
+        std::string name = dirent->d_name;
         if (name == "." || name == "..") continue;
         entries.emplace_back(name, dirent->d_ino,
 #ifdef HAVE_STRUCT_DIRENT_D_TYPE
@@ -303,7 +303,7 @@ unsigned char getFileType(const Path & path)
 }
 
 
-string readFile(int fd)
+std::string readFile(int fd)
 {
     struct stat st;
     if (fstat(fd, &st) == -1)
@@ -313,7 +313,7 @@ string readFile(int fd)
 }
 
 
-string readFile(const Path & path)
+std::string readFile(const Path & path)
 {
     AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
     if (!fd)
@@ -366,9 +366,9 @@ void writeFile(const Path & path, Source & source, mode_t mode)
     }
 }
 
-string readLine(int fd)
+std::string readLine(int fd)
 {
-    string s;
+    std::string s;
     while (1) {
         checkInterrupt();
         char ch;
@@ -387,7 +387,7 @@ string readLine(int fd)
 }
 
 
-void writeLine(int fd, string s)
+void writeLine(int fd, std::string s)
 {
     s += '\n';
     writeFull(fd, s);
@@ -398,7 +398,7 @@ static void _deletePath(int parentfd, const Path & path, uint64_t & bytesFreed)
 {
     checkInterrupt();
 
-    string name(baseNameOf(path));
+    std::string name(baseNameOf(path));
 
     struct stat st;
     if (fstatat(parentfd, name.c_str(), &st, AT_SYMLINK_NOFOLLOW) == -1) {
@@ -566,8 +566,8 @@ Path getConfigDir()
 std::vector<Path> getConfigDirs()
 {
     Path configHome = getConfigDir();
-    string configDirs = getEnv("XDG_CONFIG_DIRS").value_or("/etc/xdg");
+    auto configDirs = getEnv("XDG_CONFIG_DIRS").value_or("/etc/xdg");
-    std::vector<Path> result = tokenizeString<std::vector<string>>(configDirs, ":");
+    std::vector<Path> result = tokenizeString<std::vector<std::string>>(configDirs, ":");
     result.insert(result.begin(), configHome);
     return result;
 }
@@ -670,7 +670,7 @@ void writeFull(int fd, std::string_view s, bool allowInterrupts)
 }
 
 
-string drainFD(int fd, bool block, const size_t reserveSize)
+std::string drainFD(int fd, bool block, const size_t reserveSize)
 {
     // the parser needs two extra bytes to append terminating characters, other users will
     // not care very much about the extra memory.
@@ -719,7 +719,7 @@ void drainFD(int fd, Sink & sink, bool block)
 
 AutoDelete::AutoDelete() : del{false} {}
 
-AutoDelete::AutoDelete(const string & p, bool recursive) : path(p)
+AutoDelete::AutoDelete(const std::string & p, bool recursive) : path(p)
 {
     del = true;
     this->recursive = recursive;
@@ -1036,7 +1036,7 @@ std::vector<char *> stringsToCharPtrs(const Strings & ss)
     return res;
 }
 
-string runProgram(Path program, bool searchPath, const Strings & args,
+std::string runProgram(Path program, bool searchPath, const Strings & args,
     const std::optional<std::string> & input)
 {
     auto res = runProgram(RunOptions {.program = program, .searchPath = searchPath, .args = args, .input = input});
@@ -1238,11 +1238,11 @@ void _interrupted()
 template<class C> C tokenizeString(std::string_view s, std::string_view separators)
 {
     C result;
-    string::size_type pos = s.find_first_not_of(separators, 0);
+    auto pos = s.find_first_not_of(separators, 0);
-    while (pos != string::npos) {
+    while (pos != std::string::npos) {
-        string::size_type end = s.find_first_of(separators, pos + 1);
+        auto end = s.find_first_of(separators, pos + 1);
-        if (end == string::npos) end = s.size();
+        if (end == std::string::npos) end = s.size();
-        result.insert(result.end(), string(s, pos, end - pos));
+        result.insert(result.end(), std::string(s, pos, end - pos));
         pos = s.find_first_not_of(separators, end);
     }
     return result;
@@ -1250,29 +1250,30 @@ template<class C> C tokenizeString(std::string_view s, std::string_view separato
 
 template Strings tokenizeString(std::string_view s, std::string_view separators);
 template StringSet tokenizeString(std::string_view s, std::string_view separators);
-template std::vector<string> tokenizeString(std::string_view s, std::string_view separators);
+template std::vector<std::string> tokenizeString(std::string_view s, std::string_view separators);
 
 
-string chomp(std::string_view s)
+std::string chomp(std::string_view s)
 {
     size_t i = s.find_last_not_of(" \n\r\t");
-    return i == string::npos ? "" : string(s, 0, i + 1);
+    return i == std::string_view::npos ? "" : std::string(s, 0, i + 1);
 }
 
 
-string trim(const string & s, const string & whitespace)
+std::string trim(std::string_view s, std::string_view whitespace)
 {
     auto i = s.find_first_not_of(whitespace);
-    if (i == string::npos) return "";
+    if (i == std::string_view::npos) return "";
     auto j = s.find_last_not_of(whitespace);
-    return string(s, i, j == string::npos ? j : j - i + 1);
+    return std::string(s, i, j == std::string::npos ? j : j - i + 1);
 }
 
 
-string replaceStrings(std::string_view s,
+std::string replaceStrings(
-    const std::string & from, const std::string & to)
+    std::string res,
+    std::string_view from,
+    std::string_view to)
 {
-    string res(s);
     if (from.empty()) return res;
     size_t pos = 0;
     while ((pos = res.find(from, pos)) != std::string::npos) {
@@ -1283,20 +1284,19 @@ string replaceStrings(std::string_view s,
 }
 
 
-std::string rewriteStrings(const std::string & _s, const StringMap & rewrites)
+std::string rewriteStrings(std::string s, const StringMap & rewrites)
 {
-    auto s = _s;
     for (auto & i : rewrites) {
         if (i.first == i.second) continue;
         size_t j = 0;
-        while ((j = s.find(i.first, j)) != string::npos)
+        while ((j = s.find(i.first, j)) != std::string::npos)
             s.replace(j, i.first.size(), i.second);
     }
     return s;
 }
 
 
-string statusToString(int status)
+std::string statusToString(int status)
 {
     if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
         if (WIFEXITED(status))
@@ -1448,9 +1448,9 @@ std::string filterANSIEscapes(const std::string & s, bool filterAll, unsigned in
 
 constexpr char base64Chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
-string base64Encode(std::string_view s)
+std::string base64Encode(std::string_view s)
 {
-    string res;
+    std::string res;
     int data = 0, nbits = 0;
 
     for (char c : s) {
@@ -1469,7 +1469,7 @@ string base64Encode(std::string_view s)
 }
 
 
-string base64Decode(std::string_view s)
+std::string base64Decode(std::string_view s)
 {
     constexpr char npos = -1;
     constexpr std::array<char, 256> base64DecodeChars = [&]() {
@@ -1481,7 +1481,7 @@ string base64Decode(std::string_view s)
         return result;
     }();
 
-    string res;
+    std::string res;
     unsigned int d = 0, bits = 0;
 
     for (char c : s) {
@@ -1835,7 +1835,7 @@ void connect(int fd, const std::string & path)
 }
 
 
-string showBytes(uint64_t bytes)
+std::string showBytes(uint64_t bytes)
 {
     return fmt("%.2f MiB", bytes / (1024.0 * 1024.0));
 }
@@ -1846,7 +1846,7 @@ void commonChildInit(Pipe & logPipe)
 {
     logger = makeSimpleLogger();
 
-    const static string pathNullDevice = "/dev/null";
+    const static std::string pathNullDevice = "/dev/null";
     restoreProcessContext(false);
 
     /* Put the child in a separate session (and thus a separate

src/libutil/util.hh

@@ -92,11 +92,11 @@ bool isLink(const Path & path);
    removed. */
 struct DirEntry
 {
-    string name;
+    std::string name;
     ino_t ino;
     unsigned char type; // one of DT_*
-    DirEntry(const string & name, ino_t ino, unsigned char type)
+    DirEntry(std::string name, ino_t ino, unsigned char type)
-        : name(name), ino(ino), type(type) { }
+        : name(std::move(name)), ino(ino), type(type) { }
 };
 
 typedef std::vector<DirEntry> DirEntries;
@@ -106,8 +106,8 @@ DirEntries readDirectory(const Path & path);
 unsigned char getFileType(const Path & path);
 
 /* Read the contents of a file into a string. */
-string readFile(int fd);
+std::string readFile(int fd);
-string readFile(const Path & path);
+std::string readFile(const Path & path);
 void readFile(const Path & path, Sink & sink);
 
 /* Write a string to a file. */
@@ -116,10 +116,10 @@ void writeFile(const Path & path, std::string_view s, mode_t mode = 0666);
 void writeFile(const Path & path, Source & source, mode_t mode = 0666);
 
 /* Read a line from a file descriptor. */
-string readLine(int fd);
+std::string readLine(int fd);
 
 /* Write a line to a file descriptor. */
-void writeLine(int fd, string s);
+void writeLine(int fd, std::string s);
 
 /* Delete a path; i.e., in the case of a directory, it is deleted
    recursively. It's not an error if the path does not exist. The
@@ -170,7 +170,7 @@ MakeError(EndOfFile, Error);
 
 
 /* Read a file descriptor until EOF occurs. */
-string drainFD(int fd, bool block = true, const size_t reserveSize=0);
+std::string drainFD(int fd, bool block = true, const size_t reserveSize=0);
 
 void drainFD(int fd, Sink & sink, bool block = true);
 
@@ -268,7 +268,7 @@ void killUser(uid_t uid);
    pid to the caller. */
 struct ProcessOptions
 {
-    string errorPrefix = "";
+    std::string errorPrefix = "";
     bool dieWithParent = true;
     bool runExitHandlers = false;
     bool allowVfork = false;
@@ -279,7 +279,7 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options = P
 
 /* Run a program and return its stdout in a string (i.e., like the
    shell backtick operator). */
-string runProgram(Path program, bool searchPath = false,
+std::string runProgram(Path program, bool searchPath = false,
     const Strings & args = Strings(),
     const std::optional<std::string> & input = {});
 
@@ -378,12 +378,12 @@ template<class C> C tokenizeString(std::string_view s, std::string_view separato
 /* Concatenate the given strings with a separator between the
    elements. */
 template<class C>
-string concatStringsSep(const std::string_view sep, const C & ss)
+std::string concatStringsSep(const std::string_view sep, const C & ss)
 {
     size_t size = 0;
     // need a cast to string_view since this is also called with Symbols
     for (const auto & s : ss) size += sep.size() + std::string_view(s).size();
-    string s;
+    std::string s;
     s.reserve(size);
     for (auto & i : ss) {
         if (s.size() != 0) s += sep;
@@ -394,7 +394,7 @@ string concatStringsSep(const std::string_view sep, const C & ss)
 
 template<class ... Parts>
 auto concatStrings(Parts && ... parts)
-    -> std::enable_if_t<(... && std::is_convertible_v<Parts, std::string_view>), string>
+    -> std::enable_if_t<(... && std::is_convertible_v<Parts, std::string_view>), std::string>
 {
     std::string_view views[sizeof...(parts)] = { parts... };
     return concatStringsSep({}, views);
@@ -413,24 +413,26 @@ template<class C> Strings quoteStrings(const C & c)
 
 /* Remove trailing whitespace from a string. FIXME: return
    std::string_view. */
-string chomp(std::string_view s);
+std::string chomp(std::string_view s);
 
 
 /* Remove whitespace from the start and end of a string. */
-string trim(const string & s, const string & whitespace = " \n\r\t");
+std::string trim(std::string_view s, std::string_view whitespace = " \n\r\t");
 
 
 /* Replace all occurrences of a string inside another string. */
-string replaceStrings(std::string_view s,
+std::string replaceStrings(
-    const std::string & from, const std::string & to);
+    std::string s,
+    std::string_view from,
+    std::string_view to);
 
 
-std::string rewriteStrings(const std::string & s, const StringMap & rewrites);
+std::string rewriteStrings(std::string s, const StringMap & rewrites);
 
 
 /* Convert the exit status of a child as returned by wait() into an
    error string. */
-string statusToString(int status);
+std::string statusToString(int status);
 
 bool statusOk(int status);
 
@@ -525,8 +527,8 @@ std::string filterANSIEscapes(const std::string & s,
 
 
 /* Base64 encoding/decoding. */
-string base64Encode(std::string_view s);
+std::string base64Encode(std::string_view s);
-string base64Decode(std::string_view s);
+std::string base64Decode(std::string_view s);
 
 
 /* Remove common leading whitespace from the lines in the string

src/nix-build/nix-build.cc

@@ -32,11 +32,11 @@ extern char * * environ __attribute__((weak));
 /* Recreate the effect of the perl shellwords function, breaking up a
  * string into arguments like a shell word, including escapes
  */
-std::vector<string> shellwords(const string & s)
+static std::vector<std::string> shellwords(const std::string & s)
 {
     std::regex whitespace("^(\\s+).*");
     auto begin = s.cbegin();
-    std::vector<string> res;
+    std::vector<std::string> res;
     std::string cur;
     enum state {
         sBegin,
@@ -96,14 +96,14 @@ static void main_nix_build(int argc, char * * argv)
 
     auto inShebang = false;
     std::string script;
-    std::vector<string> savedArgs;
+    std::vector<std::string> savedArgs;
 
     AutoDelete tmpDir(createTempDir("", myName));
 
     std::string outLink = "./result";
 
     // List of environment variables kept for --pure
-    std::set<string> keepVars{
+    std::set<std::string> keepVars{
         "HOME", "XDG_RUNTIME_DIR", "USER", "LOGNAME", "DISPLAY",
         "WAYLAND_DISPLAY", "WAYLAND_SOCKET", "PATH", "TERM", "IN_NIX_SHELL",
         "NIX_SHELL_PRESERVE_PROMPT", "TZ", "PAGER", "NIX_BUILD_SHELL", "SHLVL",
@@ -384,7 +384,9 @@ static void main_nix_build(int argc, char * * argv)
         // Build or fetch all dependencies of the derivation.
         for (const auto & input : drv.inputDrvs)
             if (std::all_of(envExclude.cbegin(), envExclude.cend(),
-                    [&](const string & exclude) { return !std::regex_search(store->printStorePath(input.first), std::regex(exclude)); }))
+                    [&](const std::string & exclude) {
+                        return !std::regex_search(store->printStorePath(input.first), std::regex(exclude));
+                    }))
             {
                 pathsToBuild.push_back({input.first, input.second});
                 pathsToCopy.insert(input.first);
@@ -437,7 +439,7 @@ static void main_nix_build(int argc, char * * argv)
         for (auto & var : drv.env)
             if (passAsFile.count(var.first)) {
                 keepTmp = true;
-                string fn = ".attr-" + std::to_string(fileNr++);
+                auto fn = ".attr-" + std::to_string(fileNr++);
                 Path p = (Path) tmpDir + "/" + fn;
                 writeFile(p, var.second);
                 env[var.first + "Path"] = p;
@@ -514,7 +516,7 @@ static void main_nix_build(int argc, char * * argv)
                 (pure ? "" : "PATH=$PATH:$p; unset p; "),
                 shellEscape(dirOf(*shell)),
                 shellEscape(*shell),
-                (getenv("TZ") ? (string("export TZ=") + shellEscape(getenv("TZ")) + "; ") : ""),
+                (getenv("TZ") ? (std::string("export TZ=") + shellEscape(getenv("TZ")) + "; ") : ""),
                 envCommand);
         vomit("Sourcing nix-shell with file %s and contents:\n%s", rcfile, rc);
         writeFile(rcfile, rc);

src/nix-channel/nix-channel.cc

@@ -11,7 +11,7 @@
 
 using namespace nix;
 
-typedef std::map<string,string> Channels;
+typedef std::map<std::string, std::string> Channels;
 
 static Channels channels;
 static Path channelsList;
@@ -22,11 +22,11 @@ static void readChannels()
     if (!pathExists(channelsList)) return;
     auto channelsFile = readFile(channelsList);
 
-    for (const auto & line : tokenizeString<std::vector<string>>(channelsFile, "\n")) {
+    for (const auto & line : tokenizeString<std::vector<std::string>>(channelsFile, "\n")) {
         chomp(line);
         if (std::regex_search(line, std::regex("^\\s*\\#")))
             continue;
-        auto split = tokenizeString<std::vector<string>>(line, " ");
+        auto split = tokenizeString<std::vector<std::string>>(line, " ");
         auto url = std::regex_replace(split[0], std::regex("/*$"), "");
         auto name = split.size() > 1 ? split[1] : std::string(baseNameOf(url));
         channels[name] = url;
@@ -44,7 +44,7 @@ static void writeChannels()
 }
 
 // Adds a channel.
-static void addChannel(const string & url, const string & name)
+static void addChannel(const std::string & url, const std::string & name)
 {
     if (!regex_search(url, std::regex("^(file|http|https)://")))
         throw Error("invalid channel URL '%1%'", url);
@@ -58,7 +58,7 @@ static void addChannel(const string & url, const string & name)
 static Path profile;
 
 // Remove a channel.
-static void removeChannel(const string & name)
+static void removeChannel(const std::string & name)
 {
     readChannels();
     channels.erase(name);
@@ -96,7 +96,7 @@ static void update(const StringSet & channelNames)
         std::smatch match;
         auto urlBase = std::string(baseNameOf(url));
         if (std::regex_search(urlBase, match, std::regex("(-\\d.*)$")))
-            cname = cname + (string) match[1];
+            cname = cname + (std::string) match[1];
 
         std::string extraAttrs;
 
@@ -176,7 +176,7 @@ static int main_nix_channel(int argc, char ** argv)
             cUpdate,
             cRollback
         } cmd = cNone;
-        std::vector<string> args;
+        std::vector<std::string> args;
         parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
             if (*arg == "--help") {
                 showManPage("nix-channel");

src/nix-collect-garbage/nix-collect-garbage.cc

@@ -36,7 +36,7 @@ void removeOldGenerations(std::string dir)
             } catch (SysError & e) {
                 if (e.errNo == ENOENT) continue;
             }
-            if (link.find("link") != string::npos) {
+            if (link.find("link") != std::string::npos) {
                 printInfo(format("removing old generations of profile %1%") % path);
                 if (deleteOlderThan != "")
                     deleteGenerationsOlderThan(path, deleteOlderThan, dryRun);

src/nix-env/nix-env.cc

@@ -46,7 +46,7 @@ struct InstallSourceInfo
     InstallSourceType type;
     Path nixExprPath; /* for srcNixExprDrvs, srcNixExprs */
     Path profile; /* for srcProfile */
-    string systemFilter; /* for srcNixExprDrvs */
+    std::string systemFilter; /* for srcNixExprDrvs */
     Bindings * autoArgs;
 };
 
@@ -59,7 +59,7 @@ struct Globals
     bool dryRun;
     bool preserveInstalled;
     bool removeAll;
-    string forceName;
+    std::string forceName;
     bool prebuiltOnly;
 };
 
@@ -68,8 +68,8 @@ typedef void (* Operation) (Globals & globals,
     Strings opFlags, Strings opArgs);
 
 
-static string needArg(Strings::iterator & i,
+static std::string needArg(Strings::iterator & i,
-    Strings & args, const string & arg)
+    Strings & args, const std::string & arg)
 {
     if (i == args.end()) throw UsageError("'%1%' requires an argument", arg);
     return *i++;
@@ -77,7 +77,7 @@ static string needArg(Strings::iterator & i,
 
 
 static bool parseInstallSourceOptions(Globals & globals,
-    Strings::iterator & i, Strings & args, const string & arg)
+    Strings::iterator & i, Strings & args, const std::string & arg)
 {
     if (arg == "--from-expression" || arg == "-E")
         globals.instSource.type = srcNixExprs;
@@ -124,9 +124,9 @@ static void getAllExprs(EvalState & state,
                otherwise the attribute cannot be selected with the
                `-A' option.  Useful if you want to stick a Nix
                expression directly in ~/.nix-defexpr. */
-            string attrName = i;
+            std::string attrName = i;
             if (hasSuffix(attrName, ".nix"))
-                attrName = string(attrName, 0, attrName.size() - 4);
+                attrName = std::string(attrName, 0, attrName.size() - 4);
             if (!seen.insert(attrName).second) {
                 printError("warning: name collision in input Nix expressions, skipping '%1%'", path2);
                 continue;
@@ -175,8 +175,8 @@ static void loadSourceExpr(EvalState & state, const Path & path, Value & v)
 
 
 static void loadDerivations(EvalState & state, Path nixExprPath,
-    string systemFilter, Bindings & autoArgs,
+    std::string systemFilter, Bindings & autoArgs,
-    const string & pathPrefix, DrvInfos & elems)
+    const std::string & pathPrefix, DrvInfos & elems)
 {
     Value vRoot;
     loadSourceExpr(state, nixExprPath, vRoot);
@@ -360,9 +360,9 @@ static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
 }
 
 
-static bool isPath(const string & s)
+static bool isPath(std::string_view s)
 {
-    return s.find('/') != string::npos;
+    return s.find('/') != std::string_view::npos;
 }
 
 
@@ -433,8 +433,8 @@ static void queryInstSources(EvalState & state,
                     auto outputs = state.store->queryDerivationOutputMap(path);
                     elem.setOutPath(state.store->printStorePath(outputs.at("out")));
                     if (name.size() >= drvExtension.size() &&
-                        string(name, name.size() - drvExtension.size()) == drvExtension)
+                        std::string(name, name.size() - drvExtension.size()) == drvExtension)
-                        name = string(name, 0, name.size() - drvExtension.size());
+                        name = name.substr(0, name.size() - drvExtension.size());
                 }
                 else elem.setOutPath(state.store->printStorePath(path));
 
@@ -515,7 +515,7 @@ static void installDerivations(Globals & globals,
 
 
     while (true) {
-        string lockToken = optimisticLockProfile(profile);
+        auto lockToken = optimisticLockProfile(profile);
 
         DrvInfos allElems(newElems);
 
@@ -551,7 +551,7 @@ static void installDerivations(Globals & globals,
 static void opInstall(Globals & globals, Strings opFlags, Strings opArgs)
 {
     for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
-        string arg = *i++;
+        auto arg = *i++;
         if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
         else if (arg == "--preserve-installed" || arg == "-P")
             globals.preserveInstalled = true;
@@ -578,7 +578,7 @@ static void upgradeDerivations(Globals & globals,
        name and a higher version number. */
 
     while (true) {
-        string lockToken = optimisticLockProfile(globals.profile);
+        auto lockToken = optimisticLockProfile(globals.profile);
 
         DrvInfos installedElems = queryInstalled(*globals.state, globals.profile);
 
@@ -606,7 +606,7 @@ static void upgradeDerivations(Globals & globals,
                    take the one with the highest version.
                    Do not upgrade if it would decrease the priority. */
                 DrvInfos::iterator bestElem = availElems.end();
-                string bestVersion;
+                std::string bestVersion;
                 for (auto j = availElems.begin(); j != availElems.end(); ++j) {
                     if (comparePriorities(*globals.state, i, *j) > 0)
                         continue;
@@ -662,7 +662,7 @@ static void opUpgrade(Globals & globals, Strings opFlags, Strings opArgs)
 {
     UpgradeType upgradeType = utLt;
     for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
-        string arg = *i++;
+        std::string arg = *i++;
         if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
         else if (arg == "--lt") upgradeType = utLt;
         else if (arg == "--leq") upgradeType = utLeq;
@@ -676,7 +676,7 @@ static void opUpgrade(Globals & globals, Strings opFlags, Strings opArgs)
 
 
 static void setMetaFlag(EvalState & state, DrvInfo & drv,
-    const string & name, const string & value)
+    const std::string & name, const std::string & value)
 {
     auto v = state.allocValue();
     v->mkString(value);
@@ -692,12 +692,12 @@ static void opSetFlag(Globals & globals, Strings opFlags, Strings opArgs)
         throw UsageError("not enough arguments to '--set-flag'");
 
     Strings::iterator arg = opArgs.begin();
-    string flagName = *arg++;
+    std::string flagName = *arg++;
-    string flagValue = *arg++;
+    std::string flagValue = *arg++;
     DrvNames selectors = drvNamesFromArgs(Strings(arg, opArgs.end()));
 
     while (true) {
-        string lockToken = optimisticLockProfile(globals.profile);
+        std::string lockToken = optimisticLockProfile(globals.profile);
 
         DrvInfos installedElems = queryInstalled(*globals.state, globals.profile);
 
@@ -728,7 +728,7 @@ static void opSet(Globals & globals, Strings opFlags, Strings opArgs)
     if (!store2) throw Error("--set is not supported for this Nix store");
 
     for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
-        string arg = *i++;
+        std::string arg = *i++;
         if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
         else throw UsageError("unknown flag '%1%'", arg);
     }
@@ -769,7 +769,7 @@ static void uninstallDerivations(Globals & globals, Strings & selectors,
     Path & profile)
 {
     while (true) {
-        string lockToken = optimisticLockProfile(profile);
+        auto lockToken = optimisticLockProfile(profile);
 
         DrvInfos workingElems = queryInstalled(*globals.state, profile);
 
@@ -855,11 +855,11 @@ void printTable(Table & table)
         Strings::iterator j;
         size_t column;
         for (j = i.begin(), column = 0; j != i.end(); ++j, ++column) {
-            string s = *j;
+            std::string s = *j;
             replace(s.begin(), s.end(), '\n', ' ');
             cout << s;
             if (column < nrColumns - 1)
-                cout << string(widths[column] - s.size() + 2, ' ');
+                cout << std::string(widths[column] - s.size() + 2, ' ');
         }
         cout << std::endl;
     }
@@ -876,7 +876,7 @@ void printTable(Table & table)
 typedef enum { cvLess, cvEqual, cvGreater, cvUnavail } VersionDiff;
 
 static VersionDiff compareVersionAgainstSet(
-    const DrvInfo & elem, const DrvInfos & elems, string & version)
+    const DrvInfo & elem, const DrvInfos & elems, std::string & version)
 {
     DrvName name(elem.queryName());
 
@@ -958,7 +958,7 @@ static void queryJSON(Globals & globals, std::vector<DrvInfo> & elems, bool prin
 static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
 {
     Strings remaining;
-    string attrPath;
+    std::string attrPath;
 
     bool printStatus = false;
     bool printName = true;
@@ -977,7 +977,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
     settings.readOnlyMode = true; /* makes evaluation a bit faster */
 
     for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
-        string arg = *i++;
+        auto arg = *i++;
         if (arg == "--status" || arg == "-s") printStatus = true;
         else if (arg == "--no-name") printName = false;
         else if (arg == "--system") printSystem = true;
@@ -1094,7 +1094,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                     attrs["substitutable"] = hasSubs ? "1" : "0";
                 } else
                     columns.push_back(
-                        (string) (isInstalled ? "I" : "-")
+                        (std::string) (isInstalled ? "I" : "-")
                         + (isValid ? "P" : "-")
                         + (hasSubs ? "S" : "-"));
             }
@@ -1118,7 +1118,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                    same named packages in either the set of available
                    elements, or the set of installed elements.  !!!
                    This is O(N * M), should be O(N * lg M). */
-                string version;
+                std::string version;
                 VersionDiff diff = compareVersionAgainstSet(i, otherElems, version);
 
                 char ch;
@@ -1136,7 +1136,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                         attrs["maxComparedVersion"] = version;
                     }
                 } else {
-                    string column = (string) "" + ch + " " + version;
+                    auto column = (std::string) "" + ch + " " + version;
                     if (diff == cvGreater && tty)
                         column = ANSI_RED + column + ANSI_NORMAL;
                     columns.push_back(column);
@@ -1150,7 +1150,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                 columns.push_back(i.querySystem());
 
             if (printDrvPath) {
-                string drvPath = i.queryDrvPath();
+                auto drvPath = i.queryDrvPath();
                 if (xmlOutput) {
                     if (drvPath != "") attrs["drvPath"] = drvPath;
                 } else
@@ -1159,7 +1159,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
 
             if (printOutPath && !xmlOutput) {
                 DrvInfo::Outputs outputs = i.queryOutputs();
-                string s;
+                std::string s;
                 for (auto & j : outputs) {
                     if (!s.empty()) s += ';';
                     if (j.first != "out") { s += j.first; s += "="; }
@@ -1169,7 +1169,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
             }
 
             if (printDescription) {
-                string descr = i.queryMetaString("description");
+                auto descr = i.queryMetaString("description");
                 if (xmlOutput) {
                     if (descr != "") attrs["description"] = descr;
                 } else
@@ -1331,12 +1331,12 @@ static void opDeleteGenerations(Globals & globals, Strings opFlags, Strings opAr
 
     if (opArgs.size() == 1 && opArgs.front() == "old") {
         deleteOldGenerations(globals.profile, globals.dryRun);
-    } else if (opArgs.size() == 1 && opArgs.front().find('d') != string::npos) {
+    } else if (opArgs.size() == 1 && opArgs.front().find('d') != std::string::npos) {
         deleteGenerationsOlderThan(globals.profile, opArgs.front(), globals.dryRun);
-    } else if (opArgs.size() == 1 && opArgs.front().find('+') != string::npos) {
+    } else if (opArgs.size() == 1 && opArgs.front().find('+') != std::string::npos) {
         if (opArgs.front().size() < 2)
             throw Error("invalid number of generations '%1%'", opArgs.front());
-        string str_max = string(opArgs.front(), 1, opArgs.front().size());
+        auto str_max = opArgs.front().substr(1);
         auto max = string2Int<GenerationNumber>(str_max);
         if (!max || *max == 0)
             throw Error("invalid number of generations to keep '%1%'", opArgs.front());
@@ -1366,7 +1366,7 @@ static int main_nix_env(int argc, char * * argv)
         Strings opFlags, opArgs;
         Operation op = 0;
         RepairFlag repair = NoRepair;
-        string file;
+        std::string file;
 
         Globals globals;
 

src/nix-env/user-env.cc

@@ -32,7 +32,7 @@ DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
 
 bool createUserEnv(EvalState & state, DrvInfos & elems,
     const Path & profile, bool keepDerivations,
-    const string & lockToken)
+    const std::string & lockToken)
 {
     /* Build the components in the user environment, if they don't
        exist already. */