X-Git-Url: http://git.tdb.fi/?p=libs%2Fcore.git;a=blobdiff_plain;f=source%2Fstrings%2Flexicalcast.h;h=13eab45f0b81c9311381f43f880caf2abb5fcf5b;hp=b6cba3b89498c32b86576c66087d9472a0a4c680;hb=e83bcaa01b98b600171886ff6b06d884385dd0ed;hpb=c7afef88380ebebc8c2b04e48664d73281ec8848

diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index b6cba3b..13eab45 100644
--- a/source/strings/lexicalcast.h
+++ b/source/strings/lexicalcast.h
@@ -4,12 +4,13 @@
 #include <sstream>
 #include <string>
 #include <stdexcept>
+#include <msp/core/meta.h>
 #include "fmt.h"
 
 namespace Msp {
 
 /**
-Thrown for errors in lexical conversions
+Thrown for errors in lexical conversions.
 */
 class lexical_error: public std::runtime_error
 {
@@ -19,6 +20,9 @@ public:
 };
 
 
+/**
+Thrown when the format is unsuitable for the type being converted.
+*/
 class format_mismatch: public lexical_error
 {
 public:
@@ -34,14 +38,15 @@ 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 &);
 };
 
@@ -88,8 +93,29 @@ void operator>>(const LexicalConverter &, std::string &);
 
 // Generic operators using stringstream
 
+struct CheckFormattedOutput: Sfinae
+{
+	static std::ostream &s;
+	template<typename T>
+	static Yes f(int (*)[sizeof(s<<T())]);
+	using Sfinae::f;
+};
+
+struct CheckFormattedInput: Sfinae
+{
+	static std::istream &s;
+	template<typename T>
+	static Yes f(int (*)[sizeof(s>>reinterpret_cast<T &>(s))]);
+	using Sfinae::f;
+};
+
+template<typename T> struct HasFormattedOutput: Sfinae::Evaluate<CheckFormattedOutput, T> { };
+template<typename T> struct HasFormattedInput: Sfinae::Evaluate<CheckFormattedInput, T> { };
+
+
 template<typename T>
-void operator<<(LexicalConverter &c, const T &v)
+typename EnableIf<HasFormattedOutput<T>::value, void>::Yes
+operator<<(LexicalConverter &c, const T &v)
 {
 	std::ostringstream ss;
 	ss<<c.get_fmt()<<v;
@@ -97,7 +123,8 @@ 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);
@@ -106,23 +133,54 @@ 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();
+	}
+};
+
+/** Perform a lexical conversion between a string and another type.  The source
+type can normally be deduced by the compiler, so this can be used just like the
+standard C++ casts.  A format may additionally be specified to force a specific
+interpretation. */
+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