Make lexical_cast symmetric

[libs/core.git] / source / strings / lexicalcast.h

diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index b6cba3b89498c32b86576c66087d9472a0a4c680..c6a17da3491d053b6460399fddea6473ea1ca839 100644 (file)
--- a/source/strings/lexicalcast.h
+++ b/source/strings/lexicalcast.h
@@ -106,23 +106,51 @@ void operator>>(const LexicalConverter &c, T &v)
                throw lexical_error("conversion failure");
 }
 
-// The main interface to the lexical conversion machinery
+// Helper struct to provide partial template specialization
+
+template<typename T, typename F>
+struct LexicalCast;
 
 template<typename T>
-inline T lexical_cast(const std::string &s, const Fmt &f = Fmt())
+struct LexicalCast<T, std::string>
 {
-       LexicalConverter conv(s, f);
-       T result;
-       conv>>result;
-       return result;
-}
+       static T cast(const std::string &s, const Fmt &f = Fmt())
+       {
+               LexicalConverter conv(s, f);
+               T result;
+               conv>>result;
+               return result;
+       }
+};
 
-template<typename T>
-inline std::string lexical_cast(const T &v, const Fmt &f = Fmt())
+template<typename F>
+struct LexicalCast<std::string, F>
+{
+       static std::string cast(const F &v, const Fmt &f = Fmt())
+       {
+               LexicalConverter conv(f);
+               conv<<v;
+               return conv.get();
+       }
+};
+
+template<>
+struct LexicalCast<std::string, std::string>
+{
+       static std::string cast(const std::string &v, const Fmt &f = Fmt())
+       {
+               LexicalConverter conv(f);
+               conv<<v;
+               return conv.get();
+       }
+};
+
+// The main interface to the lexical conversion machinery
+
+template<typename T, typename F>
+inline T lexical_cast(const F &v, const Fmt &f = Fmt())
 {
-       LexicalConverter conv(f);
-       conv<<v;
-       return conv.get();
+       return LexicalCast<T, F>::cast(v, f);
 }
 
 } // namespace Msp