Simplify the SFINAE construct a bit

[libs/core.git] / source / strings / lexicalcast.h

diff --git a/source/strings/lexicalcast.h b/source/strings/lexicalcast.h
index 25e3268126bde5d65cf19dca35d188c96dcebb5e..13eab45f0b81c9311381f43f880caf2abb5fcf5b 100644 (file)
--- a/source/strings/lexicalcast.h
+++ b/source/strings/lexicalcast.h
@@ -10,7 +10,7 @@
 namespace Msp {
 
 /**
-Thrown for errors in lexical conversions
+Thrown for errors in lexical conversions.
 */
 class lexical_error: public std::runtime_error
 {
@@ -20,6 +20,9 @@ public:
 };
 
 
+/**
+Thrown when the format is unsuitable for the type being converted.
+*/
 class format_mismatch: public lexical_error
 {
 public:
@@ -90,36 +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
@@ -141,8 +133,9 @@ 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;
 
@@ -180,8 +173,10 @@ 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())
 {