Replace a bunch of craft with type_traits

include/fmt/core.h

@@ -336,47 +336,13 @@ inline void require_wchar() {
       "formatting of wide characters into a narrow output is disallowed");
 }
 
-using yes = char[1];
-using no = char[2];
-
-yes &convert(unsigned long long);
-no &convert(...);
-
-template<typename T, bool ENABLE_CONVERSION>
-struct convert_to_int_impl {
-  enum { value = ENABLE_CONVERSION };
-};
-
-template<typename T, bool ENABLE_CONVERSION>
-struct convert_to_int_impl2 {
-  enum { value = false };
-};
-
-template<typename T>
-struct convert_to_int_impl2<T, true> {
-  enum {
-    // Don't convert arithmetic types.
-    value = convert_to_int_impl<T, !std::is_arithmetic<T>::value>::value
-  };
-};
-
-template<typename T>
+template <typename T, bool ENABLE = true>
 struct convert_to_int {
   enum {
-    enable_conversion = sizeof(convert(std::declval<T>())) == sizeof(yes)
+    value = !std::is_arithmetic<T>::value && std::is_convertible<T, int>::value
   };
-  enum { value = convert_to_int_impl2<T, enable_conversion>::value };
 };
 
-#define FMT_DISABLE_CONVERSION_TO_INT(Type) \
-  template <> \
-  struct convert_to_int<Type> { enum { value = 0 }; }
-
-// Silence warnings about convering float to int.
-FMT_DISABLE_CONVERSION_TO_INT(float);
-FMT_DISABLE_CONVERSION_TO_INT(double);
-FMT_DISABLE_CONVERSION_TO_INT(long double);
-
 template <typename Char>
 struct named_arg_base;