Make convert_to_int public (#818)

include/fmt/core.h

@@ -341,6 +341,13 @@ class basic_format_args;
 template <typename T, typename Char = char, typename Enable = void>
 struct formatter;
 
+template <typename T, typename Char, typename Enable = void>
+struct convert_to_int {
+  enum {
+    value = !std::is_arithmetic<T>::value && std::is_convertible<T, int>::value
+  };
+};
+
 namespace internal {
 
 /** A contiguous memory buffer with an optional growing ability. */
@@ -490,13 +497,6 @@ FMT_CONSTEXPR bool is_arithmetic(type t) {
   return t > internal::none_type && t <= internal::last_numeric_type;
 }
 
-template <typename T, typename Char, bool ENABLE = true>
-struct convert_to_int {
-  enum {
-    value = !std::is_arithmetic<T>::value && std::is_convertible<T, int>::value
-  };
-};
-
 template <typename Char>
 struct string_value {
   const Char *value;

include/fmt/ostream.h

@@ -71,15 +71,6 @@ class is_streamable {
   static const bool value = result::value;
 };
 
-// Disable conversion to int if T has an overloaded operator<< which is a free
-// function (not a member of std::ostream).
-template <typename T, typename Char>
-class convert_to_int<T, Char, true> {
- public:
-  static const bool value =
-    convert_to_int<T, Char, false>::value && !is_streamable<T, Char>::value;
-};
-
 // Write the content of buf to os.
 template <typename Char>
 void write(std::basic_ostream<Char> &os, basic_buffer<Char> &buf) {
@@ -106,6 +97,15 @@ void format_value(basic_buffer<Char> &buffer, const T &value) {
 }
 }  // namespace internal
 
+// Disable conversion to int if T has an overloaded operator<< which is a free
+// function (not a member of std::ostream).
+template <typename T, typename Char>
+struct convert_to_int<T, Char, void> {
+  static const bool value =
+    convert_to_int<T, Char, int>::value &&
+    !internal::is_streamable<T, Char>::value;
+};
+
 // Formats an object of type T that has an overloaded ostream operator<<.
 template <typename T, typename Char>
 struct formatter<T, Char,