X-Git-Url: http://git.tdb.fi/?p=libs%2Fcore.git;a=blobdiff_plain;f=source%2Fstrings%2Flexicalcast.h;h=25e3268126bde5d65cf19dca35d188c96dcebb5e;hp=b41654d1537a822f8a13af2d1a0616a4761d0e2f;hb=468ec9f6554c89b52e10a280411c9b9d99ef451b;hpb=4a38eb20402936497cbb75527dd7a7b321f51415

diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index b41654d..25e3268 100644
--- a/source/strings/lexicalcast.h
+++ b/source/strings/lexicalcast.h
@@ -1,16 +1,10 @@
-/* $Id$
-
-This file is part of libmspstrings
-Copyright © 2006-2008 Mikko Rasa
-Distributed under the LGPL
-*/
-
 #ifndef MSP_STRINGS_LEXICALCAST_H_
 #define MSP_STRINGS_LEXICALCAST_H_
 
 #include <sstream>
 #include <string>
 #include <stdexcept>
+#include <msp/core/meta.h>
 #include "fmt.h"
 
 namespace Msp {
@@ -41,14 +35,15 @@ class LexicalConverter
 {
 private:
 	Fmt fmt;
+	bool filled;
 	std::string buf;
 
 public:
-	LexicalConverter(const Fmt &f): fmt(f) { }
-	LexicalConverter(const std::string &s, const Fmt &f): fmt(f), buf(s) { }
+	LexicalConverter(const Fmt &f): fmt(f), filled(false) { }
+	LexicalConverter(const std::string &s, const Fmt &f): fmt(f), filled(true), buf(s) { }
 
 	const Fmt &get_fmt() const { return fmt; }
-	const std::string &get() const { return buf; }
+	const std::string &get() const;
 	void result(const std::string &);
 };
 
@@ -96,7 +91,39 @@ void operator>>(const LexicalConverter &, std::string &);
 // Generic operators using stringstream
 
 template<typename T>
-void operator<<(LexicalConverter &c, const T &v)
+struct HasFormattedOutput: Sfinae
+{
+	static std::ostream &s;
+	static T &v;
+
+	/* The expression must depend on the template parameter, or the compiler
+	will give an error. */
+	template<typename U>
+	static Yes f(int (*)[sizeof(s<<HasFormattedOutput<U>::v)]);
+	template<typename U>
+	static No f(...);
+
+	enum { value = Evaluate<sizeof(f<T>(0))>::value };
+};
+
+template<typename T>
+struct HasFormattedInput: Sfinae
+{
+	static std::istream &s;
+	static T &v;
+
+	template<typename U>
+	static Yes f(int (*)[sizeof(s>>HasFormattedOutput<U>::v)]);
+	template<typename U>
+	static No f(...);
+
+	enum { value = Evaluate<sizeof(f<T>(0))>::value };
+};
+
+
+template<typename T>
+typename EnableIf<HasFormattedOutput<T>::value, void>::Yes
+operator<<(LexicalConverter &c, const T &v)
 {
 	std::ostringstream ss;
 	ss<<c.get_fmt()<<v;
@@ -104,7 +131,8 @@ void operator<<(LexicalConverter &c, const T &v)
 }
 
 template<typename T>
-void operator>>(const LexicalConverter &c, T &v)
+typename EnableIf<HasFormattedInput<T>::value, void>::Yes
+operator>>(const LexicalConverter &c, T &v)
 {
 	std::istringstream ss(c.get());
 	ss.setf(std::ios_base::fmtflags(0), std::ios_base::skipws);
@@ -113,23 +141,51 @@ 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