X-Git-Url: http://git.tdb.fi/?p=libs%2Fcore.git;a=blobdiff_plain;f=source%2Fstrings%2Flexicalcast.h;h=2ed0621291858c0d0f4d40fb37036fd5decc5700;hp=c6a17da3491d053b6460399fddea6473ea1ca839;hb=ea901644ac2d36256d1f38c7a3adaaee787fe1b9;hpb=42ff7c629b2aa7411963bdcc2259a06b1d1de6d3

diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index c6a17da..2ed0621 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 &);
 };
 
@@ -89,7 +94,39 @@ 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 +134,8 @@ 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);
@@ -106,8 +144,9 @@ void operator>>(const LexicalConverter &c, T &v)
 		throw lexical_error("conversion failure");
 }
 
-// Helper struct to provide partial template specialization
-
+/**
+Helper struct to provide partial template specialization.
+*/
 template<typename T, typename F>
 struct LexicalCast;
 
@@ -145,8 +184,10 @@ struct LexicalCast<std::string, std::string>
 	}
 };
 
-// The main interface to the lexical conversion machinery
-
+/** 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())
 {