From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 24 May 2019 16:57:22 +0000 (+0300)
Subject: Simplify the SFINAE construct a bit
X-Git-Url: http://git.tdb.fi/?p=libs%2Fcore.git;a=commitdiff_plain;h=e83bcaa01b98b600171886ff6b06d884385dd0ed

Simplify the SFINAE construct a bit

More of the common stuff is now stored in the helper struct.
---

diff --git a/source/core/meta.h b/source/core/meta.h
index a13f5cb..d6ca359 100644
--- a/source/core/meta.h
+++ b/source/core/meta.h
@@ -43,10 +43,13 @@ struct Sfinae
 	struct Yes { char c[2]; };
 	struct No { char c; };
 
-	template<size_t s>
+	template<typename T>
+	static No f(...);
+
+	template<typename C, typename T>
 	struct Evaluate
 	{
-		enum { value = (s==sizeof(Yes)) };
+		enum { value = (sizeof(C::template f<T>(0))==sizeof(Yes)) };
 	};
 };
 
diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index 2ed0621..13eab45 100644
--- a/source/strings/lexicalcast.h
+++ b/source/strings/lexicalcast.h
@@ -93,36 +93,25 @@ void operator>>(const LexicalConverter &, std::string &);
 
 // Generic operators using stringstream
 
-template<typename T>
-struct HasFormattedOutput: Sfinae
+struct CheckFormattedOutput: 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>
+	static Yes f(int (*)[sizeof(s<<T())]);
+	using Sfinae::f;
 };
 
-template<typename T>
-struct HasFormattedInput: Sfinae
+struct CheckFormattedInput: 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>
+	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>
 typename EnableIf<HasFormattedOutput<T>::value, void>::Yes