diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 6835c512c..0c9e69fe8 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -289,10 +289,10 @@ void SourceExprCommand::completeInstallable(AddCompletions & completions, std::s
 
             if (v2.type() == nAttrs) {
                 for (auto & i : *v2.attrs()) {
-                    std::string name = state->symbols[i.name];
+                    std::string_view name = state->symbols[i.name];
                     if (name.find(searchWord) == 0) {
                         if (prefix_ == "")
-                            completions.add(name);
+                            completions.add(std::string(name));
                         else
                             completions.add(prefix_ + "." + name);
                     }
diff --git a/src/libexpr-c/nix_api_value.cc b/src/libexpr-c/nix_api_value.cc
index 2f2f99617..cb5d9ee89 100644
--- a/src/libexpr-c/nix_api_value.cc
+++ b/src/libexpr-c/nix_api_value.cc
@@ -383,7 +383,7 @@ nix_value * nix_get_attr_byidx(
     try {
         auto & v = check_value_in(value);
         const nix::Attr & a = (*v.attrs())[i];
-        *name = ((const std::string &) (state->state.symbols[a.name])).c_str();
+        *name = state->state.symbols[a.name].c_str();
         nix_gc_incref(nullptr, a.value);
         state->state.forceValue(*a.value, nix::noPos);
         return as_nix_value_ptr(a.value);
@@ -399,7 +399,7 @@ nix_get_attr_name_byidx(nix_c_context * context, const nix_value * value, EvalSt
     try {
         auto & v = check_value_in(value);
         const nix::Attr & a = (*v.attrs())[i];
-        return ((const std::string &) (state->state.symbols[a.name])).c_str();
+        return state->state.symbols[a.name].c_str();
     }
     NIXC_CATCH_ERRS_NULL
 }
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 9ad201b63..d61d93630 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -76,7 +76,7 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
             if (!a) {
                 std::set<std::string> attrNames;
                 for (auto & attr : *v->attrs())
-                    attrNames.insert(state.symbols[attr.name]);
+                    attrNames.insert(std::string(state.symbols[attr.name]));
 
                 auto suggestions = Suggestions::bestMatches(attrNames, attr);
                 throw AttrPathNotFound(suggestions, "attribute '%1%' in selection path '%2%' not found", attr, attrPath);
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 2630c34d5..46dd3691c 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -484,7 +484,7 @@ Suggestions AttrCursor::getSuggestionsForAttr(Symbol name)
     auto attrNames = getAttrs();
     std::set<std::string> strAttrNames;
     for (auto & name : attrNames)
-        strAttrNames.insert(root->state.symbols[name]);
+        strAttrNames.insert(std::string(root->state.symbols[name]));
 
     return Suggestions::bestMatches(strAttrNames, root->state.symbols[name]);
 }
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 2a0862123..efca9dd2f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -633,11 +633,11 @@ void mapStaticEnvBindings(const SymbolTable & st, const StaticEnv & se, const En
         if (se.isWith && !env.values[0]->isThunk()) {
             // add 'with' bindings.
             for (auto & j : *env.values[0]->attrs())
-                vm[st[j.name]] = j.value;
+                vm.insert_or_assign(std::string(st[j.name]), j.value);
         } else {
             // iterate through staticenv bindings and add them.
             for (auto & i : se.vars)
-                vm[st[i.first]] = env.values[i.second];
+                vm.insert_or_assign(std::string(st[i.first]), env.values[i.second]);
         }
     }
 }
@@ -1338,7 +1338,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                 if (!(j = vAttrs->attrs()->get(name))) {
                     std::set<std::string> allAttrNames;
                     for (auto & attr : *vAttrs->attrs())
-                        allAttrNames.insert(state.symbols[attr.name]);
+                        allAttrNames.insert(std::string(state.symbols[attr.name]));
                     auto suggestions = Suggestions::bestMatches(allAttrNames, state.symbols[name]);
                     state.error<EvalError>("attribute '%1%' missing", state.symbols[name])
                         .atPos(pos).withSuggestions(suggestions).withFrame(env, *this).debugThrow();
@@ -1496,7 +1496,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                         if (!lambda.formals->has(i.name)) {
                             std::set<std::string> formalNames;
                             for (auto & formal : lambda.formals->formals)
-                                formalNames.insert(symbols[formal.name]);
+                                formalNames.insert(std::string(symbols[formal.name]));
                             auto suggestions = Suggestions::bestMatches(formalNames, symbols[i.name]);
                             error<TypeError>("function '%1%' called with unexpected argument '%2%'",
                                              (lambda.name ? std::string(symbols[lambda.name]) : "anonymous lambda"),
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 896733423..7041a3932 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -342,9 +342,9 @@ std::optional<PackageInfo> getDerivation(EvalState & state, Value & v,
 }
 
 
-static std::string addToPath(const std::string & s1, const std::string & s2)
+static std::string addToPath(const std::string & s1, std::string_view s2)
 {
-    return s1.empty() ? s2 : s1 + "." + s2;
+    return s1.empty() ? std::string(s2) : s1 + "." + s2;
 }
 
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 134363e1a..bcde0bb12 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1225,7 +1225,7 @@ static void derivationStrictInternal(
 
     for (auto & i : attrs->lexicographicOrder(state.symbols)) {
         if (i->name == state.sIgnoreNulls) continue;
-        const std::string & key = state.symbols[i->name];
+        auto key = state.symbols[i->name];
         vomit("processing attribute '%1%'", key);
 
         auto handleHashMode = [&](const std::string_view s) {
@@ -1309,7 +1309,7 @@ static void derivationStrictInternal(
 
                     if (i->name == state.sStructuredAttrs) continue;
 
-                    (*jsonObject)[key] = printValueAsJSON(state, true, *i->value, pos, context);
+                    jsonObject->emplace(key, printValueAsJSON(state, true, *i->value, pos, context));
 
                     if (i->name == state.sBuilder)
                         drv.builder = state.forceString(*i->value, context, pos, context_below);
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
index 967a186dd..5c2821492 100644
--- a/src/libexpr/symbol-table.hh
+++ b/src/libexpr/symbol-table.hh
@@ -30,9 +30,9 @@ public:
         return *s == s2;
     }
 
-    operator const std::string & () const
+    const char * c_str() const
     {
-        return *s;
+        return s->c_str();
     }
 
     operator const std::string_view () const
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 936ecf078..f8cc05616 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -58,7 +58,7 @@ json printValueAsJSON(EvalState & state, bool strict,
                 out = json::object();
                 for (auto & a : v.attrs()->lexicographicOrder(state.symbols)) {
                     try {
-                        out[state.symbols[a->name]] = printValueAsJSON(state, strict, *a->value, a->pos, context, copyToStore);
+                        out.emplace(state.symbols[a->name], printValueAsJSON(state, strict, *a->value, a->pos, context, copyToStore));
                     } catch (Error & e) {
                         e.addTrace(state.positions[a->pos],
                             HintFmt("while evaluating attribute '%1%'", state.symbols[a->name]));
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index 1de8cdf84..9734ebec4 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -9,7 +9,7 @@
 namespace nix {
 
 
-static XMLAttrs singletonAttrs(const std::string & name, const std::string & value)
+static XMLAttrs singletonAttrs(const std::string & name, std::string_view value)
 {
     XMLAttrs attrs;
     attrs[name] = value;
diff --git a/src/libflake/flake/flake.cc b/src/libflake/flake/flake.cc
index 6f47b5992..eb083fcee 100644
--- a/src/libflake/flake/flake.cc
+++ b/src/libflake/flake/flake.cc
@@ -98,7 +98,7 @@ static std::map<FlakeId, FlakeInput> parseFlakeInputs(
     const std::optional<Path> & baseDir, InputPath lockRootPath);
 
 static FlakeInput parseFlakeInput(EvalState & state,
-    const std::string & inputName, Value * value, const PosIdx pos,
+    std::string_view inputName, Value * value, const PosIdx pos,
     const std::optional<Path> & baseDir, InputPath lockRootPath)
 {
     expectType(state, nAttrs, *value, pos);
@@ -178,7 +178,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
     }
 
     if (!input.follows && !input.ref)
-        input.ref = FlakeRef::fromAttrs({{"type", "indirect"}, {"id", inputName}});
+        input.ref = FlakeRef::fromAttrs({{"type", "indirect"}, {"id", std::string(inputName)}});
 
     return input;
 }
@@ -244,7 +244,7 @@ static Flake readFlake(
             for (auto & formal : outputs->value->payload.lambda.fun->formals->formals) {
                 if (formal.name != state.sSelf)
                     flake.inputs.emplace(state.symbols[formal.name], FlakeInput {
-                        .ref = parseFlakeRef(state.symbols[formal.name])
+                        .ref = parseFlakeRef(std::string(state.symbols[formal.name]))
                     });
             }
         }
diff --git a/src/libutil/suggestions.cc b/src/libutil/suggestions.cc
index e67e986fb..84c8e296f 100644
--- a/src/libutil/suggestions.cc
+++ b/src/libutil/suggestions.cc
@@ -38,8 +38,8 @@ int levenshteinDistance(std::string_view first, std::string_view second)
 }
 
 Suggestions Suggestions::bestMatches (
-    std::set<std::string> allMatches,
-    std::string query)
+    const std::set<std::string> & allMatches,
+    std::string_view query)
 {
     std::set<Suggestion> res;
     for (const auto & possibleMatch : allMatches) {
diff --git a/src/libutil/suggestions.hh b/src/libutil/suggestions.hh
index 9abf5ee5f..17d1d69c1 100644
--- a/src/libutil/suggestions.hh
+++ b/src/libutil/suggestions.hh
@@ -35,8 +35,8 @@ public:
     ) const;
 
     static Suggestions bestMatches (
-        std::set<std::string> allMatches,
-        std::string query
+        const std::set<std::string> & allMatches,
+        std::string_view query
     );
 
     Suggestions& operator+=(const Suggestions & other);
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 84c659023..b65c7f59d 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -165,7 +165,7 @@ struct CmdFlakeLock : FlakeCommand
 };
 
 static void enumerateOutputs(EvalState & state, Value & vFlake,
-    std::function<void(const std::string & name, Value & vProvide, const PosIdx pos)> callback)
+    std::function<void(std::string_view name, Value & vProvide, const PosIdx pos)> callback)
 {
     auto pos = vFlake.determinePos(noPos);
     state.forceAttrs(vFlake, pos, "while evaluating a flake to get its outputs");
@@ -393,15 +393,15 @@ struct CmdFlakeCheck : FlakeCommand
                 || (hasPrefix(name, "_") && name.substr(1) == expected);
         };
 
-        auto checkSystemName = [&](const std::string & system, const PosIdx pos) {
+        auto checkSystemName = [&](std::string_view system, const PosIdx pos) {
             // FIXME: what's the format of "system"?
             if (system.find('-') == std::string::npos)
                 reportError(Error("'%s' is not a valid system type, at %s", system, resolve(pos)));
         };
 
-        auto checkSystemType = [&](const std::string & system, const PosIdx pos) {
+        auto checkSystemType = [&](std::string_view system, const PosIdx pos) {
             if (!checkAllSystems && system != localSystem) {
-                omittedSystems.insert(system);
+                omittedSystems.insert(std::string(system));
                 return false;
             } else {
                 return true;
@@ -450,7 +450,7 @@ struct CmdFlakeCheck : FlakeCommand
             }
         };
 
-        auto checkOverlay = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
+        auto checkOverlay = [&](std::string_view attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlInfo, actUnknown,
                     fmt("checking overlay '%s'", attrPath));
@@ -469,7 +469,7 @@ struct CmdFlakeCheck : FlakeCommand
             }
         };
 
-        auto checkModule = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
+        auto checkModule = [&](std::string_view attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlInfo, actUnknown,
                     fmt("checking NixOS module '%s'", attrPath));
@@ -480,9 +480,9 @@ struct CmdFlakeCheck : FlakeCommand
             }
         };
 
-        std::function<void(const std::string & attrPath, Value & v, const PosIdx pos)> checkHydraJobs;
+        std::function<void(std::string_view attrPath, Value & v, const PosIdx pos)> checkHydraJobs;
 
-        checkHydraJobs = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
+        checkHydraJobs = [&](std::string_view attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlInfo, actUnknown,
                     fmt("checking Hydra job '%s'", attrPath));
@@ -523,7 +523,7 @@ struct CmdFlakeCheck : FlakeCommand
             }
         };
 
-        auto checkTemplate = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
+        auto checkTemplate = [&](std::string_view attrPath, Value & v, const PosIdx pos) {
             try {
                 Activity act(*logger, lvlInfo, actUnknown,
                     fmt("checking template '%s'", attrPath));
@@ -579,7 +579,7 @@ struct CmdFlakeCheck : FlakeCommand
 
             enumerateOutputs(*state,
                 *vFlake,
-                [&](const std::string & name, Value & vOutput, const PosIdx pos) {
+                [&](std::string_view name, Value & vOutput, const PosIdx pos) {
                     Activity act(*logger, lvlInfo, actUnknown,
                         fmt("checking flake output '%s'", name));
 
@@ -603,7 +603,7 @@ struct CmdFlakeCheck : FlakeCommand
                         if (name == "checks") {
                             state->forceAttrs(vOutput, pos, "");
                             for (auto & attr : *vOutput.attrs()) {
-                                const auto & attr_name = state->symbols[attr.name];
+                                std::string_view attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
                                 if (checkSystemType(attr_name, attr.pos)) {
                                     state->forceAttrs(*attr.value, attr.pos, "");
diff --git a/src/nix/main.cc b/src/nix/main.cc
index c90bb25a7..775052351 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -429,7 +429,7 @@ void mainWrapped(int argc, char * * argv)
             b["doc"] = trim(stripIndentation(primOp->doc));
             if (primOp->experimentalFeature)
                 b["experimental-feature"] = primOp->experimentalFeature;
-            builtinsJson[state.symbols[builtin.name]] = std::move(b);
+            builtinsJson.emplace(state.symbols[builtin.name], std::move(b));
         }
         for (auto & [name, info] : state.constantInfos) {
             auto b = nlohmann::json::object();