X-Git-Url: http://git.tdb.fi/?p=libs%2Fcore.git;a=blobdiff_plain;f=source%2Fstrings%2Flexicalcast.h;h=80963f44dd3a233ff2d16b01ec007935d01e73c9;hp=c6a17da3491d053b6460399fddea6473ea1ca839;hb=ff0d3252cad08280b9c320b3fea5a11c80406c23;hpb=42ff7c629b2aa7411963bdcc2259a06b1d1de6d3

diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index c6a17da..80963f4 100644
--- a/source/strings/lexicalcast.h
+++ b/source/strings/lexicalcast.h
@@ -4,6 +4,7 @@
 #include <sstream>
 #include <string>
 #include <stdexcept>
+#include <msp/core/meta.h>
 #include "fmt.h"
 
 namespace Msp {
@@ -89,7 +90,39 @@ 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;
@@ -97,7 +130,8 @@ 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);