cmStringAlgorithms: Add faster cmJoin overloads for strings

cmJoin() is often used with std::string ranges. Generic implementation
uses std::ostringstream which is not optimal. With strings we can avoid
operator<<() and make much faster implementation. Additional 'initial'
argument is useful for cmStringCommand.cxx:HandleAppendCommand().

1 files changed, 8 insertions, 4 deletions

diff --git a/Source/cmStringCommand.cxx b/Source/cmStringCommand.cxx
index 653b383..4000a7d 100644
--- a/Source/cmStringCommand.cxx
+++ b/Source/cmStringCommand.cxx
@@ -11,6 +11,7 @@
 #include <memory>
 
 #include <cm/iterator>
+#include <cm/string_view>
 #include <cmext/string_view>
 
 #include "cmsys/RegularExpression.hxx"
@@ -534,11 +535,14 @@ bool HandleAppendCommand(std::vector<std::string> const& args,
     return true;
   }
 
-  const std::string& variable = args[1];
+  auto const& variableName = args[1];
+
+  cm::string_view oldView{ status.GetMakefile().GetSafeDefinition(
+    variableName) };
+
+  auto const newValue = cmJoin(cmMakeRange(args).advance(2), {}, oldView);
+  status.GetMakefile().AddDefinition(variableName, newValue);
 
-  std::string value = status.GetMakefile().GetSafeDefinition(variable);
-  value += cmJoin(cmMakeRange(args).advance(2), std::string());
-  status.GetMakefile().AddDefinition(variable, value);
   return true;
 }