NixOS · Jun 18, 2019 · Jun 18, 2019
diff --git a/src/libutil/args.cc b/src/libutil/args.cc
@@ -215,17 +215,15 @@ void Command::printHelp(const string & programName, std::ostream & out)
     }
 }
 
-MultiCommand::MultiCommand(const std::vector<ref<Command>> & _commands)
+MultiCommand::MultiCommand(const Commands & commands)
+    : commands(commands)
 {
-    for (auto & command : _commands)
-        commands.emplace(command->name(), command);
-
     expectedArgs.push_back(ExpectedArg{"command", 1, true, [=](std::vector<std::string> ss) {
         assert(!command);
         auto i = commands.find(ss[0]);
         if (i == commands.end())
             throw UsageError("'%s' is not a recognised command", ss[0]);
-        command = i->second;
+        command = i->second();
     }});
 }
 
@@ -246,10 +244,11 @@ void MultiCommand::printHelp(const string & programName, std::ostream & out)
     out << "Available commands:\n";
 
     Table2 table;
-    for (auto & command : commands) {
-        auto descr = command.second->description();
+    for (auto & i : commands) {
+        auto command = i.second();
+        auto descr = command->description();
         if (!descr.empty())
-            table.push_back(std::make_pair(command.second->name(), descr));
+            table.push_back(std::make_pair(command->name(), descr));
     }
     printTable(out, table);
 }

diff --git a/src/libutil/args.hh b/src/libutil/args.hh
@@ -192,7 +192,12 @@ public:
    run() method. */
 struct Command : virtual Args
 {
-    virtual std::string name() = 0;
+private:
+    std::string _name;
+
+public:
+    std::string name() { return _name; }
+
     virtual void prepare() { };
     virtual void run() = 0;
 
@@ -209,7 +214,7 @@ struct Command : virtual Args
     void printHelp(const string & programName, std::ostream & out) override;
 };
 
-typedef std::map<std::string, ref<Command>> Commands;
+typedef std::map<std::string, std::function<ref<Command>()>> Commands;
 
 /* An argument parser that supports multiple subcommands,
    i.e. ‘<command> <subcommand>’. */
@@ -220,7 +225,7 @@ public:
 
     std::shared_ptr<Command> command;
 
-    MultiCommand(const std::vector<ref<Command>> & commands);
+    MultiCommand(const Commands & commands);
 
     void printHelp(const string & programName, std::ostream & out) override;
 

diff --git a/src/nix/add-to-store.cc b/src/nix/add-to-store.cc
@@ -22,11 +22,6 @@ struct CmdAddToStore : MixDryRun, StoreCommand
             .dest(&namePart);
     }
 
-    std::string name() override
-    {
-        return "add-to-store";
-    }
-
     std::string description() override
     {
         return "add a path to the Nix store";
@@ -58,4 +53,4 @@ struct CmdAddToStore : MixDryRun, StoreCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdAddToStore>());
+static auto r1 = registerCommand<CmdAddToStore>("add-to-store");
diff --git a/src/nix/build.cc b/src/nix/build.cc
@@ -25,11 +25,6 @@ struct CmdBuild : MixDryRun, InstallablesCommand
             .set(&outLink, Path(""));
     }
 
-    std::string name() override
-    {
-        return "build";
-    }
-
     std::string description() override
     {
         return "build a derivation or fetch a store path";
@@ -72,4 +67,4 @@ struct CmdBuild : MixDryRun, InstallablesCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdBuild>());
+static auto r1 = registerCommand<CmdBuild>("build");
diff --git a/src/nix/cat.cc b/src/nix/cat.cc
@@ -28,11 +28,6 @@ struct CmdCatStore : StoreCommand, MixCat
         expectArg("path", &path);
     }
 
-    std::string name() override
-    {
-        return "cat-store";
-    }
-
     std::string description() override
     {
         return "print the contents of a store file on stdout";
@@ -54,11 +49,6 @@ struct CmdCatNar : StoreCommand, MixCat
         expectArg("path", &path);
     }
 
-    std::string name() override
-    {
-        return "cat-nar";
-    }
-
     std::string description() override
     {
         return "print the contents of a file inside a NAR file";
@@ -70,5 +60,5 @@ struct CmdCatNar : StoreCommand, MixCat
     }
 };
 
-static RegisterCommand r1(make_ref<CmdCatStore>());
-static RegisterCommand r2(make_ref<CmdCatNar>());
+static auto r1 = registerCommand<CmdCatStore>("cat-store");
+static auto r2 = registerCommand<CmdCatNar>("cat-nar");
diff --git a/src/nix/command.cc b/src/nix/command.cc
@@ -4,7 +4,7 @@
 
 namespace nix {
 
-std::vector<ref<Command>> * RegisterCommand::commands = 0;
+Commands * RegisterCommand::commands = nullptr;
 
 StoreCommand::StoreCommand()
 {

diff --git a/src/nix/command.hh b/src/nix/command.hh
@@ -190,15 +190,22 @@ struct StorePathCommand : public InstallablesCommand
 /* A helper class for registering commands globally. */
 struct RegisterCommand
 {
-    static std::vector<ref<Command>> * commands;
+    static Commands * commands;
 
-    RegisterCommand(ref<Command> command)
+    RegisterCommand(const std::string & name,
+        std::function<ref<Command>()> command)
     {
-        if (!commands) commands = new std::vector<ref<Command>>;
-        commands->push_back(command);
+        if (!commands) commands = new Commands;
+        commands->emplace(name, command);
     }
 };
 
+template<class T>
+static RegisterCommand registerCommand(const std::string & name)
+{
+    return RegisterCommand(name, [](){ return make_ref<T>(); });
+}
+
 Buildables build(ref<Store> store, RealiseMode mode,
     std::vector<std::shared_ptr<Installable>> installables);
 

diff --git a/src/nix/copy.cc b/src/nix/copy.cc
@@ -42,11 +42,6 @@ struct CmdCopy : StorePathsCommand
             .set(&substitute, Substitute);
     }
 
-    std::string name() override
-    {
-        return "copy";
-    }
-
     std::string description() override
     {
         return "copy paths between Nix stores";
@@ -97,4 +92,4 @@ struct CmdCopy : StorePathsCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdCopy>());
+static auto r1 = registerCommand<CmdCopy>("copy");
diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
@@ -20,11 +20,6 @@ struct CmdDoctor : StoreCommand
 {
     bool success = true;
 
-    std::string name() override
-    {
-        return "doctor";
-    }
-
     std::string description() override
     {
         return "check your system for potential problems";
@@ -121,4 +116,4 @@ struct CmdDoctor : StoreCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdDoctor>());
+static auto r1 = registerCommand<CmdDoctor>("doctore");
diff --git a/src/nix/dump-path.cc b/src/nix/dump-path.cc
@@ -5,11 +5,6 @@ using namespace nix;
 
 struct CmdDumpPath : StorePathCommand
 {
-    std::string name() override
-    {
-        return "dump-path";
-    }
-
     std::string description() override
     {
         return "dump a store path to stdout (in NAR format)";
@@ -33,4 +28,4 @@ struct CmdDumpPath : StorePathCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdDumpPath>());
+static auto r1 = registerCommand<CmdDumpPath>("dump-path");
diff --git a/src/nix/edit.cc b/src/nix/edit.cc
@@ -10,11 +10,6 @@ using namespace nix;
 
 struct CmdEdit : InstallableCommand
 {
-    std::string name() override
-    {
-        return "edit";
-    }
-
     std::string description() override
     {
         return "open the Nix expression of a Nix package in $EDITOR";
@@ -78,4 +73,4 @@ struct CmdEdit : InstallableCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdEdit>());
+static auto r1 = registerCommand<CmdEdit>("edit");
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
@@ -18,11 +18,6 @@ struct CmdEval : MixJSON, InstallableCommand
         mkFlag(0, "raw", "print strings unquoted", &raw);
     }
 
-    std::string name() override
-    {
-        return "eval";
-    }
-
     std::string description() override
     {
         return "evaluate a Nix expression";
@@ -74,4 +69,4 @@ struct CmdEval : MixJSON, InstallableCommand
     }
 };
 
-static RegisterCommand r1(make_ref<CmdEval>());
+static auto r1 = registerCommand<CmdEval>("eval");