Avoid some copies

Source/cmFileMonitor.cxx

@@ -247,7 +247,10 @@ public:
 
   void StopWatching() final {}
 
-  void AppendCallback(cmFileMonitor::Callback cb) { CbList.push_back(cb); }
+  void AppendCallback(cmFileMonitor::Callback const& cb)
+  {
+    this->CbList.push_back(cb);
+  }
 
   std::string Path() const final
   {
@@ -310,7 +313,7 @@ cmFileMonitor::~cmFileMonitor()
 }
 
 void cmFileMonitor::MonitorPaths(const std::vector<std::string>& paths,
-                                 Callback cb)
+                                 Callback const& cb)
 {
   for (const auto& p : paths) {
     std::vector<std::string> pathSegments;

Source/cmFileMonitor.h

@@ -17,7 +17,7 @@ public:
   ~cmFileMonitor();
 
   using Callback = std::function<void(const std::string&, int, int)>;
-  void MonitorPaths(const std::vector<std::string>& paths, Callback cb);
+  void MonitorPaths(const std::vector<std::string>& paths, Callback const& cb);
   void StopMonitoring();
 
   std::vector<std::string> WatchedFiles() const;

Source/cmGlobalUnixMakefileGenerator3.cxx

@@ -963,7 +963,7 @@ void cmGlobalUnixMakefileGenerator3::WriteHelpRule(
             (type == cmStateEnums::OBJECT_LIBRARY) ||
             (type == cmStateEnums::GLOBAL_TARGET) ||
             (type == cmStateEnums::UTILITY)) {
-          std::string name = target->GetName();
+          std::string const& name = target->GetName();
           if (emittedTargets.insert(name).second) {
             path = "... ";
             path += name;

Source/cmOutputRequiredFilesCommand.cxx

@@ -180,26 +180,23 @@ protected:
     while (cmSystemTools::GetLineFromStream(fin, line)) {
       if (cmHasLiteralPrefix(line.c_str(), "#include")) {
         // if it is an include line then create a string class
-        std::string currentline = line;
-        size_t qstart = currentline.find('\"', 8);
+        size_t qstart = line.find('\"', 8);
         size_t qend;
         // if a quote is not found look for a <
         if (qstart == std::string::npos) {
-          qstart = currentline.find('<', 8);
+          qstart = line.find('<', 8);
           // if a < is not found then move on
           if (qstart == std::string::npos) {
-            cmSystemTools::Error("unknown include directive ",
-                                 currentline.c_str());
+            cmSystemTools::Error("unknown include directive ", line.c_str());
             continue;
           } else {
-            qend = currentline.find('>', qstart + 1);
+            qend = line.find('>', qstart + 1);
           }
         } else {
-          qend = currentline.find('\"', qstart + 1);
+          qend = line.find('\"', qstart + 1);
         }
         // extract the file being included
-        std::string includeFile =
-          currentline.substr(qstart + 1, qend - qstart - 1);
+        std::string includeFile = line.substr(qstart + 1, qend - qstart - 1);
         // see if the include matches the regular expression
         if (!this->IncludeFileRegularExpression.find(includeFile)) {
           if (this->Verbose) {

Source/cmServerProtocol.cxx

@@ -82,7 +82,7 @@ static void getCMakeInputs(const cmGlobalGenerator* gg,
                            std::vector<std::string>* tmpFiles)
 {
   const std::string cmakeRootDir = cmSystemTools::GetCMakeRoot() + '/';
-  const std::vector<cmMakefile*> makefiles = gg->GetMakefiles();
+  std::vector<cmMakefile*> const& makefiles = gg->GetMakefiles();
   for (auto it = makefiles.begin(); it != makefiles.end(); ++it) {
     const std::vector<std::string> listFiles = (*it)->GetListFiles();
 
@@ -850,7 +850,7 @@ static Json::Value DumpTargetsList(
   return result;
 }
 
-static Json::Value DumpProjectList(const cmake* cm, const std::string config)
+static Json::Value DumpProjectList(const cmake* cm, std::string const& config)
 {
   Json::Value result = Json::arrayValue;
 
@@ -1059,7 +1059,7 @@ cmServerResponse cmServerProtocol1_0::ProcessGlobalSettings(
 }
 
 static void setBool(const cmServerRequest& request, const std::string& key,
-                    std::function<void(bool)> setter)
+                    std::function<void(bool)> const& setter)
 {
   if (request.Data[key].isNull()) {
     return;