integral_constant -> bool_constant

include/fmt/core.h

@@ -400,7 +400,7 @@ using fmt::v5::to_string_view;
 
 // Specifies whether S is a string type convertible to fmt::basic_string_view.
 // It should be a constexpr function but MSVC 2017 fails to compile it in
-// enable_if.
+// enable_if. MSVC 2015 fails to compile it as an alias template.
 template <typename S>
 struct is_string
     : bool_constant<
@@ -483,8 +483,7 @@ struct formatter {
 };
 
 template <typename T, typename Char, typename Enable = void>
-struct convert_to_int
-    : std::integral_constant<bool, !std::is_arithmetic<T>::value &&
+struct convert_to_int : bool_constant<!std::is_arithmetic<T>::value &&
                                       std::is_convertible<T, int>::value> {};
 
 namespace internal {

include/fmt/format.h

@@ -780,8 +780,8 @@ inline char8_t to_char8_t(char c) { return static_cast<char8_t>(c); }
 
 template <typename InputIt, typename OutChar>
 struct needs_conversion
-    : std::integral_constant<
-          bool, std::is_same<typename std::iterator_traits<InputIt>::value_type,
+    : bool_constant<
+          std::is_same<typename std::iterator_traits<InputIt>::value_type,
                        char>::value &&
           std::is_same<OutChar, char8_t>::value> {};
 
@@ -2261,9 +2261,7 @@ void check_format_string(S format_str) {
 // It is not possible to use get_type in formatter specialization directly
 // because of a bug in MSVC.
 template <typename Context, typename T>
-struct format_type
-    : std::integral_constant<bool, get_type<Context, T>::value != custom_type> {
-};
+using format_type = bool_constant<get_type<Context, T>::value != custom_type>;
 
 template <template <typename> class Handler, typename Spec, typename Context>
 void handle_dynamic_spec(Spec& value, arg_ref<typename Context::char_type> ref,