Simplify char_t

fmtlib · Jan 5, 2024 · 7ef3c1a · 7ef3c1a
1 parent a5d4c2b
commit 7ef3c1a
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Showing 2 changed files with 15 additions and 14 deletions.
diff --git a/include/fmt/core.h b/include/fmt/core.h
@@ -570,9 +570,9 @@ template <> struct is_char<char> : std::true_type {};
 
 namespace detail {
 
-// Constructs fmt::basic_string_view<Char> from types **implicitly** convertible
-// to it, deducing Char. Explicitly convertible types such as compile-time
-// strings are intentionally excluded.
+// Constructs fmt::basic_string_view<Char> from types implicitly convertible
+// to it, deducing Char. Explicitly convertible types such as the ones returned
+// from FMT_STRING are intentionally excluded.
 template <typename Char, FMT_ENABLE_IF(is_char<Char>::value)>
 FMT_INLINE auto to_string_view(const Char* s) -> basic_string_view<Char> {
   return s;
@@ -597,12 +597,6 @@ template <typename S, typename = void>
 struct is_string
     : std::is_class<decltype(detail::to_string_view(std::declval<S>()))> {};
 
-template <typename S, typename = void> struct char_t_impl {};
-template <typename S> struct char_t_impl<S, enable_if_t<is_string<S>::value>> {
-  using result = decltype(to_string_view(std::declval<S>()));
-  using type = typename result::value_type;
-};
-
 enum class type {
   none_type,
   // Integer types should go first,
@@ -682,7 +676,9 @@ enum {
 FMT_NORETURN FMT_API void throw_format_error(const char* message);
 
 /** String's character type. */
-template <typename S> using char_t = typename detail::char_t_impl<S>::type;
+template <typename S>
+using char_t =
+    typename decltype(detail::to_string_view(std::declval<S>()))::value_type;
 
 /**
   \rst
@@ -1423,8 +1419,10 @@ template <typename Context> struct arg_mapper {
     return val;
   }
   template <typename T,
-            FMT_ENABLE_IF(is_string<T>::value && !std::is_pointer<T>::value &&
-                          std::is_same<char_type, char_t<T>>::value)>
+            typename Char =
+                typename decltype(detail::to_string_view(T()))::value_type,
+            FMT_ENABLE_IF(!std::is_pointer<T>::value &&
+                          std::is_same<Char, char_type>::value)>
   FMT_CONSTEXPR FMT_INLINE auto map(const T& val)
       -> basic_string_view<char_type> {
     return to_string_view(val);

diff --git a/include/fmt/xchar.h b/include/fmt/xchar.h
@@ -30,8 +30,11 @@ enum char8_type : unsigned char {};
 template <typename T>
 using is_exotic_char = bool_constant<!std::is_same<T, char>::value>;
 
-template <typename S, typename = void>
-struct format_string_char : char_t_impl<S> {};
+template <typename S, typename = void> struct format_string_char {};
+
+template <typename S> struct format_string_char<S, void_t<char_t<S>>> {
+  using type = char_t<S>;
+};
 
 template <typename S>
 struct format_string_char<S, enable_if_t<is_compile_string<S>::value>> {