Use template structs instead of phantoms

src/libstore/build.cc

@@ -1864,11 +1864,11 @@ HookReply DerivationGoal::tryBuildHook()
 
     /* Tell the hook all the inputs that have to be copied to the
        remote system. */
-    nix::worker_proto::write(worker.store, hook->sink, inputPaths);
+    WorkerProto<StorePathSet>::write(worker.store, hook->sink, inputPaths);
 
     /* Tell the hooks the missing outputs that have to be copied back
        from the remote system. */
-    nix::worker_proto::write(worker.store, hook->sink, missingPaths);
+    WorkerProto<StorePathSet>::write(worker.store, hook->sink, missingPaths);
 
     hook->sink = FdSink();
     hook->toHook.writeSide = -1;

src/libstore/daemon.cc

@@ -256,11 +256,11 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQueryValidPaths: {
-        auto paths = nix::worker_proto::read(*store, from, Phantom<StorePathSet> {});
+        auto paths = WorkerProto<StorePathSet>::read(*store, from);
         logger->startWork();
         auto res = store->queryValidPaths(paths);
         logger->stopWork();
-        nix::worker_proto::write(*store, to, res);
+        WorkerProto<StorePathSet>::write(*store, to, res);
         break;
     }
 
@@ -276,11 +276,11 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopQuerySubstitutablePaths: {
-        auto paths = nix::worker_proto::read(*store, from, Phantom<StorePathSet> {});
+        auto paths = WorkerProto<StorePathSet>::read(*store, from);
         logger->startWork();
         auto res = store->querySubstitutablePaths(paths);
         logger->stopWork();
-        nix::worker_proto::write(*store, to, res);
+        WorkerProto<StorePathSet>::write(*store, to, res);
         break;
     }
 
@@ -309,7 +309,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
             paths = store->queryValidDerivers(path);
         else paths = store->queryDerivationOutputs(path);
         logger->stopWork();
-        nix::worker_proto::write(*store, to, paths);
+        WorkerProto<StorePathSet>::write(*store, to, paths);
         break;
     }
 
@@ -327,7 +327,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         auto outputs = store->queryDerivationOutputMap(path);
         logger->stopWork();
-        nix::worker_proto::write(*store, to, outputs);
+        WorkerProto<std::map<std::string, std::optional<StorePath>>>::write(*store, to, outputs);
         break;
     }
 
@@ -397,7 +397,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopAddTextToStore: {
         string suffix = readString(from);
         string s = readString(from);
-        auto refs = nix::worker_proto::read(*store, from, Phantom<StorePathSet> {});
+        auto refs = WorkerProto<StorePathSet>::read(*store, from);
         logger->startWork();
         auto path = store->addTextToStore(suffix, s, refs, NoRepair);
         logger->stopWork();
@@ -518,7 +518,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopCollectGarbage: {
         GCOptions options;
         options.action = (GCOptions::GCAction) readInt(from);
-        options.pathsToDelete = nix::worker_proto::read(*store, from, Phantom<StorePathSet> {});
+        options.pathsToDelete = WorkerProto<StorePathSet>::read(*store, from);
         from >> options.ignoreLiveness >> options.maxFreed;
         // obsolete fields
         readInt(from);
@@ -587,7 +587,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         else {
             to << 1
                << (i->second.deriver ? store->printStorePath(*i->second.deriver) : "");
-            nix::worker_proto::write(*store, to, i->second.references);
+            WorkerProto<StorePathSet>::write(*store, to, i->second.references);
             to << i->second.downloadSize
                << i->second.narSize;
         }
@@ -598,11 +598,11 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         SubstitutablePathInfos infos;
         StorePathCAMap pathsMap = {};
         if (GET_PROTOCOL_MINOR(clientVersion) < 22) {
-            auto paths = nix::worker_proto::read(*store, from, Phantom<StorePathSet> {});
+            auto paths = WorkerProto<StorePathSet>::read(*store, from);
             for (auto & path : paths)
                 pathsMap.emplace(path, std::nullopt);
         } else
-            pathsMap = nix::worker_proto::read(*store, from, Phantom<StorePathCAMap> {});
+            pathsMap = WorkerProto<StorePathCAMap>::read(*store, from);
         logger->startWork();
         store->querySubstitutablePathInfos(pathsMap, infos);
         logger->stopWork();
@@ -610,7 +610,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         for (auto & i : infos) {
             to << store->printStorePath(i.first)
                << (i.second.deriver ? store->printStorePath(*i.second.deriver) : "");
-            nix::worker_proto::write(*store, to, i.second.references);
+            WorkerProto<StorePathSet>::write(*store, to, i.second.references);
             to << i.second.downloadSize << i.second.narSize;
         }
         break;
@@ -620,7 +620,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         auto paths = store->queryAllValidPaths();
         logger->stopWork();
-        nix::worker_proto::write(*store, to, paths);
+        WorkerProto<StorePathSet>::write(*store, to, paths);
         break;
     }
 
@@ -639,7 +639,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 to << 1;
             to << (info->deriver ? store->printStorePath(*info->deriver) : "")
                << info->narHash->to_string(Base16, false);
-            nix::worker_proto::write(*store, to, info->references);
+            WorkerProto<StorePathSet>::write(*store, to, info->references);
             to << info->registrationTime << info->narSize;
             if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
                 to << info->ultimate
@@ -699,7 +699,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (deriver != "")
             info.deriver = store->parseStorePath(deriver);
         info.narHash = Hash::parseAny(readString(from), htSHA256);
-        info.references = nix::worker_proto::read(*store, from, Phantom<StorePathSet> {});
+        info.references = WorkerProto<StorePathSet>::read(*store, from);
         from >> info.registrationTime >> info.narSize >> info.ultimate;
         info.sigs = readStrings<StringSet>(from);
         info.ca = parseContentAddressOpt(readString(from));
@@ -799,9 +799,9 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         uint64_t downloadSize, narSize;
         store->queryMissing(targets, willBuild, willSubstitute, unknown, downloadSize, narSize);
         logger->stopWork();
-        nix::worker_proto::write(*store, to, willBuild);
+        WorkerProto<StorePathSet>::write(*store, to, willBuild);
-        nix::worker_proto::write(*store, to, willSubstitute);
+        WorkerProto<StorePathSet>::write(*store, to, willSubstitute);
-        nix::worker_proto::write(*store, to, unknown);
+        WorkerProto<StorePathSet>::write(*store, to, unknown);
         to << downloadSize << narSize;
         break;
     }

src/libstore/derivations.cc

@@ -605,7 +605,7 @@ Source & readDerivation(Source & in, const Store & store, BasicDerivation & drv,
         drv.outputs.emplace(std::move(name), std::move(output));
     }
 
-    drv.inputSrcs = nix::worker_proto::read(store, in, Phantom<StorePathSet> {});
+    drv.inputSrcs = WorkerProto<StorePathSet>::read(store, in);
     in >> drv.platform >> drv.builder;
     drv.args = readStrings<Strings>(in);
 
@@ -640,7 +640,7 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
             },
         }, i.second.output);
     }
-    nix::worker_proto::write(store, out, drv.inputSrcs);
+    WorkerProto<StorePathSet>::write(store, out, drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
     out << drv.env.size();
     for (auto & i : drv.env)

src/libstore/export-import.cc

@@ -45,7 +45,7 @@ void Store::exportPath(const StorePath & path, Sink & sink)
     teeSink
         << exportMagic
         << printStorePath(path);
-    nix::worker_proto::write(*this, teeSink, info->references);
+    WorkerProto<StorePathSet>::write(*this, teeSink, info->references);
     teeSink
         << (info->deriver ? printStorePath(*info->deriver) : "")
         << 0;
@@ -73,7 +73,7 @@ StorePaths Store::importPaths(Source & source, CheckSigsFlag checkSigs)
 
         //Activity act(*logger, lvlInfo, format("importing path '%s'") % info.path);
 
-        info.references = nix::worker_proto::read(*this, source, Phantom<StorePathSet> {});
+        info.references = WorkerProto<StorePathSet>::read(*this, source);
 
         auto deriver = readString(source);
         if (deriver != "")

src/libstore/legacy-ssh-store.cc

@@ -107,7 +107,7 @@ struct LegacySSHStore : public Store
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info->deriver = parseStorePath(deriver);
-            info->references = nix::worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+            info->references = WorkerProto<StorePathSet>::read(*this, conn->from);
             readLongLong(conn->from); // download size
             info->narSize = readLongLong(conn->from);
 
@@ -139,7 +139,7 @@ struct LegacySSHStore : public Store
                 << printStorePath(info.path)
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << info.narHash->to_string(Base16, false);
-            nix::worker_proto::write(*this, conn->to, info.references);
+            WorkerProto<StorePathSet>::write(*this, conn->to, info.references);
             conn->to
                 << info.registrationTime
                 << info.narSize
@@ -168,7 +168,7 @@ struct LegacySSHStore : public Store
             conn->to
                 << exportMagic
                 << printStorePath(info.path);
-            nix::worker_proto::write(*this, conn->to, info.references);
+            WorkerProto<StorePathSet>::write(*this, conn->to, info.references);
             conn->to
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0
@@ -251,10 +251,10 @@ struct LegacySSHStore : public Store
         conn->to
             << cmdQueryClosure
             << includeOutputs;
-        nix::worker_proto::write(*this, conn->to, paths);
+        WorkerProto<StorePathSet>::write(*this, conn->to, paths);
         conn->to.flush();
 
-        for (auto & i : nix::worker_proto::read(*this, conn->from, Phantom<StorePathSet> {}))
+        for (auto & i : WorkerProto<StorePathSet>::read(*this, conn->from))
             out.insert(i);
     }
 
@@ -267,10 +267,10 @@ struct LegacySSHStore : public Store
             << cmdQueryValidPaths
             << false // lock
             << maybeSubstitute;
-        nix::worker_proto::write(*this, conn->to, paths);
+        WorkerProto<StorePathSet>::write(*this, conn->to, paths);
         conn->to.flush();
 
-        return nix::worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        return WorkerProto<StorePathSet>::read(*this, conn->from);
     }
 
     void connect() override

src/libstore/remote-store.cc

@@ -22,40 +22,36 @@
 
 namespace nix {
 
-namespace worker_proto {
+std::string WorkerProto<std::string>::read(const Store & store, Source & from)
-
-std::string read(const Store & store, Source & from, Phantom<std::string> _)
 {
     return readString(from);
 }
 
-void write(const Store & store, Sink & out, const std::string & str)
+void WorkerProto<std::string>::write(const Store & store, Sink & out, const std::string & str)
 {
     out << str;
 }
 
-StorePath read(const Store & store, Source & from, Phantom<StorePath> _)
+StorePath WorkerProto<StorePath>::read(const Store & store, Source & from)
 {
     return store.parseStorePath(readString(from));
 }
 
-void write(const Store & store, Sink & out, const StorePath & storePath)
+void WorkerProto<StorePath>::write(const Store & store, Sink & out, const StorePath & storePath)
 {
     out << store.printStorePath(storePath);
 }
 
-ContentAddress read(const Store & store, Source & from, Phantom<ContentAddress> _)
+ContentAddress WorkerProto<ContentAddress>::read(const Store & store, Source & from)
 {
     return parseContentAddress(readString(from));
 }
 
-void write(const Store & store, Sink & out, const ContentAddress & ca)
+void WorkerProto<ContentAddress>::write(const Store & store, Sink & out, const ContentAddress & ca)
 {
     out << renderContentAddress(ca);
 }
 
-}
-
 
 /* TODO: Separate these store impls into different files, give them better names */
 RemoteStore::RemoteStore(const Params & params)
@@ -290,9 +286,9 @@ StorePathSet RemoteStore::queryValidPaths(const StorePathSet & paths, Substitute
         return res;
     } else {
         conn->to << wopQueryValidPaths;
-        nix::worker_proto::write(*this, conn->to, paths);
+        WorkerProto<StorePathSet>::write(*this, conn->to, paths);
         conn.processStderr();
-        return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        return WorkerProto<StorePathSet>::read(*this, conn->from);
     }
 }
 
@@ -302,7 +298,7 @@ StorePathSet RemoteStore::queryAllValidPaths()
     auto conn(getConnection());
     conn->to << wopQueryAllValidPaths;
     conn.processStderr();
-    return nix::worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+    return WorkerProto<StorePathSet>::read(*this, conn->from);
 }
 
 
@@ -319,9 +315,9 @@ StorePathSet RemoteStore::querySubstitutablePaths(const StorePathSet & paths)
         return res;
     } else {
         conn->to << wopQuerySubstitutablePaths;
-        nix::worker_proto::write(*this, conn->to, paths);
+        WorkerProto<StorePathSet>::write(*this, conn->to, paths);
         conn.processStderr();
-        return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        return WorkerProto<StorePathSet>::read(*this, conn->from);
     }
 }
 
@@ -343,7 +339,7 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info.deriver = parseStorePath(deriver);
-            info.references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+            info.references = WorkerProto<StorePathSet>::read(*this, conn->from);
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
             infos.insert_or_assign(i.first, std::move(info));
@@ -356,9 +352,9 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
             StorePathSet paths;
             for (auto & path : pathsMap)
                 paths.insert(path.first);
-            worker_proto::write(*this, conn->to, paths);
+            WorkerProto<StorePathSet>::write(*this, conn->to, paths);
         } else
-            worker_proto::write(*this, conn->to, pathsMap);
+            WorkerProto<StorePathCAMap>::write(*this, conn->to, pathsMap);
         conn.processStderr();
         size_t count = readNum<size_t>(conn->from);
         for (size_t n = 0; n < count; n++) {
@@ -366,7 +362,7 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
             auto deriver = readString(conn->from);
             if (deriver != "")
                 info.deriver = parseStorePath(deriver);
-            info.references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+            info.references = WorkerProto<StorePathSet>::read(*this, conn->from);
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
         }
@@ -399,7 +395,7 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
             auto deriver = readString(conn->from);
             if (deriver != "") info->deriver = parseStorePath(deriver);
             info->narHash = Hash::parseAny(readString(conn->from), htSHA256);
-            info->references = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+            info->references = WorkerProto<StorePathSet>::read(*this, conn->from);
             conn->from >> info->registrationTime >> info->narSize;
             if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
                 conn->from >> info->ultimate;
@@ -418,7 +414,7 @@ void RemoteStore::queryReferrers(const StorePath & path,
     auto conn(getConnection());
     conn->to << wopQueryReferrers << printStorePath(path);
     conn.processStderr();
-    for (auto & i : worker_proto::read(*this, conn->from, Phantom<StorePathSet> {}))
+    for (auto & i : WorkerProto<StorePathSet>::read(*this, conn->from))
         referrers.insert(i);
 }
 
@@ -428,7 +424,7 @@ StorePathSet RemoteStore::queryValidDerivers(const StorePath & path)
     auto conn(getConnection());
     conn->to << wopQueryValidDerivers << printStorePath(path);
     conn.processStderr();
-    return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+    return WorkerProto<StorePathSet>::read(*this, conn->from);
 }
 
 
@@ -440,7 +436,7 @@ StorePathSet RemoteStore::queryDerivationOutputs(const StorePath & path)
     }
     conn->to << wopQueryDerivationOutputs << printStorePath(path);
     conn.processStderr();
-    return worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+    return WorkerProto<StorePathSet>::read(*this, conn->from);
 }
 
 
@@ -449,8 +445,7 @@ std::map<std::string, std::optional<StorePath>> RemoteStore::queryDerivationOutp
     auto conn(getConnection());
     conn->to << wopQueryDerivationOutputMap << printStorePath(path);
     conn.processStderr();
-    return worker_proto::read(*this, conn->from, Phantom<std::map<std::string, std::optional<StorePath>>> {});
+    return WorkerProto<std::map<std::string, std::optional<StorePath>>>::read(*this, conn->from);
-
 }
 
 std::optional<StorePath> RemoteStore::queryPathFromHashPart(const std::string & hashPart)
@@ -479,7 +474,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
             sink
                 << exportMagic
                 << printStorePath(info.path);
-            worker_proto::write(*this, sink, info.references);
+            WorkerProto<StorePathSet>::write(*this, sink, info.references);
             sink
                 << (info.deriver ? printStorePath(*info.deriver) : "")
                 << 0 // == no legacy signature
@@ -489,7 +484,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 
         conn.processStderr(0, source2.get());
 
-        auto importedPaths = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        auto importedPaths = WorkerProto<StorePathSet>::read(*this, conn->from);
         assert(importedPaths.size() <= 1);
     }
 
@@ -498,7 +493,7 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
                  << printStorePath(info.path)
                  << (info.deriver ? printStorePath(*info.deriver) : "")
                  << info.narHash->to_string(Base16, false);
-        worker_proto::write(*this, conn->to, info.references);
+        WorkerProto<StorePathSet>::write(*this, conn->to, info.references);
         conn->to << info.registrationTime << info.narSize
                  << info.ultimate << info.sigs << renderContentAddress(info.ca)
                  << repair << !checkSigs;
@@ -631,7 +626,7 @@ StorePath RemoteStore::addTextToStore(const string & name, const string & s,
 
     auto conn(getConnection());
     conn->to << wopAddTextToStore << name << s;
-    worker_proto::write(*this, conn->to, references);
+    WorkerProto<StorePathSet>::write(*this, conn->to, references);
 
     conn.processStderr();
     return parseStorePath(readString(conn->from));
@@ -733,7 +728,7 @@ void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
 
     conn->to
         << wopCollectGarbage << options.action;
-    worker_proto::write(*this, conn->to, options.pathsToDelete);
+    WorkerProto<StorePathSet>::write(*this, conn->to, options.pathsToDelete);
     conn->to << options.ignoreLiveness
         << options.maxFreed
         /* removed options */
@@ -795,9 +790,9 @@ void RemoteStore::queryMissing(const std::vector<StorePathWithOutputs> & targets
             ss.push_back(p.to_string(*this));
         conn->to << ss;
         conn.processStderr();
-        willBuild = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        willBuild = WorkerProto<StorePathSet>::read(*this, conn->from);
-        willSubstitute = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        willSubstitute = WorkerProto<StorePathSet>::read(*this, conn->from);
-        unknown = worker_proto::read(*this, conn->from, Phantom<StorePathSet> {});
+        unknown = WorkerProto<StorePathSet>::read(*this, conn->from);
         conn->from >> downloadSize >> narSize;
         return;
     }

src/libstore/worker-protocol.hh

@@ -66,105 +66,102 @@ typedef enum {
 class Store;
 struct Source;
 
-/* To guide overloading */
 template<typename T>
-struct Phantom {};
+struct WorkerProto {
+    static T read(const Store & store, Source & from);
+    static void write(const Store & store, Sink & out, const T & t);
+};
 
+template<>
+struct WorkerProto<std::string> {
+    static std::string read(const Store & store, Source & from);
+    static void write(const Store & store, Sink & out, const std::string & t);
+};
 
-namespace worker_proto {
+template<>
-/* FIXME maybe move more stuff inside here */
+struct WorkerProto<StorePath> {
+    static StorePath read(const Store & store, Source & from);
+    static void write(const Store & store, Sink & out, const StorePath & t);
+};
 
-std::string read(const Store & store, Source & from, Phantom<std::string> _);
+template<>
-void write(const Store & store, Sink & out, const std::string & str);
+struct WorkerProto<ContentAddress> {
-
+    static ContentAddress read(const Store & store, Source & from);
-StorePath read(const Store & store, Source & from, Phantom<StorePath> _);
+    static void write(const Store & store, Sink & out, const ContentAddress & t);
-void write(const Store & store, Sink & out, const StorePath & storePath);
+};
-
-ContentAddress read(const Store & store, Source & from, Phantom<ContentAddress> _);
-void write(const Store & store, Sink & out, const ContentAddress & ca);
 
 template<typename T>
-std::set<T> read(const Store & store, Source & from, Phantom<std::set<T>> _);
+struct WorkerProto<std::set<T>> {
-template<typename T>
-void write(const Store & store, Sink & out, const std::set<T> & resSet);
 
-template<typename K, typename V>
+    static std::set<T> read(const Store & store, Source & from)
-std::map<K, V> read(const Store & store, Source & from, Phantom<std::map<K, V>> _);
-template<typename K, typename V>
-void write(const Store & store, Sink & out, const std::map<K, V> & resMap);
-
-template<typename T>
-std::optional<T> read(const Store & store, Source & from, Phantom<std::optional<T>> _);
-template<typename T>
-void write(const Store & store, Sink & out, const std::optional<T> & optVal);
-
-template<typename T>
-std::set<T> read(const Store & store, Source & from, Phantom<std::set<T>> _)
     {
         std::set<T> resSet;
         auto size = readNum<size_t>(from);
         while (size--) {
-        resSet.insert(read(store, from, Phantom<T> {}));
+            resSet.insert(WorkerProto<T>::read(store, from));
         }
         return resSet;
     }
 
-template<typename T>
+    static void write(const Store & store, Sink & out, const std::set<T> & resSet)
-void write(const Store & store, Sink & out, const std::set<T> & resSet)
     {
         out << resSet.size();
         for (auto & key : resSet) {
-        write(store, out, key);
+            WorkerProto<T>::write(store, out, key);
         }
     }
 
+};
+
 template<typename K, typename V>
-std::map<K, V> read(const Store & store, Source & from, Phantom<std::map<K, V>> _)
+struct WorkerProto<std::map<K, V>> {
+
+    static std::map<K, V> read(const Store & store, Source & from)
     {
         std::map<K, V> resMap;
         auto size = readNum<size_t>(from);
         while (size--) {
             resMap.insert_or_assign(
-            read(store, from, Phantom<K> {}),
+                WorkerProto<K>::read(store, from),
-            read(store, from, Phantom<V> {}));
+                WorkerProto<V>::read(store, from));
         }
         return resMap;
     }
 
-template<typename K, typename V>
+    static void write(const Store & store, Sink & out, const std::map<K, V> & resMap)
-void write(const Store & store, Sink & out, const std::map<K, V> & resMap)
     {
         out << resMap.size();
         for (auto & i : resMap) {
-        write(store, out, i.first);
+            WorkerProto<K>::write(store, out, i.first);
-        write(store, out, i.second);
+            WorkerProto<V>::write(store, out, i.second);
         }
     }
 
+};
+
 template<typename T>
-std::optional<T> read(const Store & store, Source & from, Phantom<std::optional<T>> _)
+struct WorkerProto<std::optional<T>> {
+
+    static std::optional<T> read(const Store & store, Source & from)
     {
         auto tag = readNum<uint8_t>(from);
         switch (tag) {
         case 0:
             return std::nullopt;
         case 1:
-        return read(store, from, Phantom<T> {});
+            return WorkerProto<T>::read(store, from);
         default:
             throw Error("got an invalid tag bit for std::optional: %#04x", (size_t)tag);
         }
     }
 
-template<typename T>
+    static void write(const Store & store, Sink & out, const std::optional<T> & optVal)
-void write(const Store & store, Sink & out, const std::optional<T> & optVal)
     {
         out << (uint64_t) (optVal ? 1 : 0);
         if (optVal)
-        nix::worker_proto::write(store, out, *optVal);
+            WorkerProto<T>::write(store, out, *optVal);
-}
-
-
     }
 
+};
 
 }

src/nix-store/nix-store.cc

@@ -815,7 +815,7 @@ static void opServe(Strings opFlags, Strings opArgs)
             case cmdQueryValidPaths: {
                 bool lock = readInt(in);
                 bool substitute = readInt(in);
-                auto paths = nix::worker_proto::read(*store, in, Phantom<StorePathSet> {});
+                auto paths = WorkerProto<StorePathSet>::read(*store, in);
                 if (lock && writeAllowed)
                     for (auto & path : paths)
                         store->addTempRoot(path);
@@ -845,19 +845,19 @@ static void opServe(Strings opFlags, Strings opArgs)
                         }
                 }
 
-                nix::worker_proto::write(*store, out, store->queryValidPaths(paths));
+                WorkerProto<StorePathSet>::write(*store, out, store->queryValidPaths(paths));
                 break;
             }
 
             case cmdQueryPathInfos: {
-                auto paths = nix::worker_proto::read(*store, in, Phantom<StorePathSet> {});
+                auto paths = WorkerProto<StorePathSet>::read(*store, in);
                 // !!! Maybe we want a queryPathInfos?
                 for (auto & i : paths) {
                     try {
                         auto info = store->queryPathInfo(i);
                         out << store->printStorePath(info->path)
                             << (info->deriver ? store->printStorePath(*info->deriver) : "");
-                        nix::worker_proto::write(*store, out, info->references);
+                        WorkerProto<StorePathSet>::write(*store, out, info->references);
                         // !!! Maybe we want compression?
                         out << info->narSize // downloadSize
                             << info->narSize;
@@ -885,7 +885,7 @@ static void opServe(Strings opFlags, Strings opArgs)
 
             case cmdExportPaths: {
                 readInt(in); // obsolete
-                store->exportPaths(nix::worker_proto::read(*store, in, Phantom<StorePathSet> {}), out);
+                store->exportPaths(WorkerProto<StorePathSet>::read(*store, in), out);
                 break;
             }
 
@@ -934,9 +934,9 @@ static void opServe(Strings opFlags, Strings opArgs)
             case cmdQueryClosure: {
                 bool includeOutputs = readInt(in);
                 StorePathSet closure;
-                store->computeFSClosure(nix::worker_proto::read(*store, in, Phantom<StorePathSet> {}),
+                store->computeFSClosure(WorkerProto<StorePathSet>::read(*store, in),
                     closure, false, includeOutputs);
-                nix::worker_proto::write(*store, out, closure);
+                WorkerProto<StorePathSet>::write(*store, out, closure);
                 break;
             }
 
@@ -949,7 +949,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 if (deriver != "")
                     info.deriver = store->parseStorePath(deriver);
                 info.narHash = Hash::parseAny(readString(in), htSHA256);
-                info.references = nix::worker_proto::read(*store, in, Phantom<StorePathSet> {});
+                info.references = WorkerProto<StorePathSet>::read(*store, in);
                 in >> info.registrationTime >> info.narSize >> info.ultimate;
                 info.sigs = readStrings<StringSet>(in);
                 info.ca = parseContentAddressOpt(readString(in));