Improve locale API

include/fmt/format-inl.h

@@ -116,7 +116,7 @@ template <typename Char> FMT_FUNC Char decimal_point_impl(locale_ref) {
 }
 #endif
 
-FMT_FUNC auto write_loc(appender out, basic_format_arg<format_context> value,
+FMT_FUNC auto write_loc(appender out, loc_value value,
                         const format_specs& specs, locale_ref loc) -> bool {
 #ifndef FMT_STATIC_THOUSANDS_SEPARATOR
   auto locale = loc.get<std::locale>();
@@ -142,11 +142,9 @@ template <typename Locale> format_facet<Locale>::format_facet(Locale& loc) {
 
 template <>
 FMT_API FMT_FUNC auto format_facet<std::locale>::do_put(
-    appender out, basic_format_arg<format_context> val,
-    const format_specs& specs) const -> bool {
-  return visit_format_arg(
-      detail::loc_writer<>{out, specs, separator_, grouping_, decimal_point_},
-      val);
+    appender out, loc_value val, const format_specs& specs) const -> bool {
+  return val.visit(
+      detail::loc_writer<>{out, specs, separator_, grouping_, decimal_point_});
 }
 #endif
 

include/fmt/format.h

@@ -1001,6 +1001,22 @@ constexpr auto compile_string_to_view(detail::std_string_view<Char> s)
 }
 }  // namespace detail_exported
 
+class loc_value {
+ private:
+  basic_format_arg<format_context> value_;
+
+ public:
+  template <typename T, FMT_ENABLE_IF(!detail::is_float128<T>::value)>
+  loc_value(T value) : value_(detail::make_arg<format_context>(value)) {}
+
+  template <typename T, FMT_ENABLE_IF(detail::is_float128<T>::value)>
+  loc_value(T) {}
+
+  template <typename Visitor> auto visit(Visitor&& vis) -> decltype(vis(0)) {
+    return visit_format_arg(vis, value_);
+  }
+};
+
 // A locale facet that formats values in UTF-8.
 // It is parameterized on the locale to avoid the heavy <locale> include.
 template <typename Locale> class format_facet : public Locale::facet {
@@ -1010,7 +1026,7 @@ template <typename Locale> class format_facet : public Locale::facet {
   std::string decimal_point_;
 
  protected:
-  virtual auto do_put(appender out, basic_format_arg<format_context> val,
+  virtual auto do_put(appender out, loc_value val,
                       const format_specs& specs) const -> bool;
 
  public:
@@ -1024,8 +1040,8 @@ template <typename Locale> class format_facet : public Locale::facet {
         grouping_(g.begin(), g.end()),
         decimal_point_(decimal_point) {}
 
-  auto put(appender out, basic_format_arg<format_context> val,
-           const format_specs& specs) const -> bool {
+  auto put(appender out, loc_value val, const format_specs& specs) const
+      -> bool {
     return do_put(out, val, specs);
   }
 };
@@ -2053,22 +2069,12 @@ auto write_int(OutputIt out, UInt value, unsigned prefix,
       });
 }
 
-template <typename T, FMT_ENABLE_IF(!is_float128<T>::value)>
-auto make_loc_value(T value) -> basic_format_arg<format_context> {
-  return make_arg<format_context>(value);
-}
-template <typename T, FMT_ENABLE_IF(is_float128<T>::value)>
-auto make_loc_value(T) -> basic_format_arg<format_context> {
-  return {};
-}
-
 // Writes a localized value.
-FMT_API auto write_loc(appender out, basic_format_arg<format_context> value,
-                       const format_specs& specs, locale_ref loc) -> bool;
-
+FMT_API auto write_loc(appender out, loc_value value, const format_specs& specs,
+                       locale_ref loc) -> bool;
 template <typename OutputIt, typename Char>
-inline auto write_loc(OutputIt, basic_format_arg<format_context>,
-                      const basic_format_specs<Char>&, locale_ref) -> bool {
+inline auto write_loc(OutputIt, loc_value, const basic_format_specs<Char>&,
+                      locale_ref) -> bool {
   return false;
 }
 
@@ -2190,8 +2196,7 @@ template <typename Char, typename OutputIt, typename T,
 FMT_CONSTEXPR FMT_INLINE auto write(OutputIt out, T value,
                                     const basic_format_specs<Char>& specs,
                                     locale_ref loc) -> OutputIt {
-  if (specs.localized && write_loc(out, make_loc_value(value), specs, loc))
-    return out;
+  if (specs.localized && write_loc(out, value, specs, loc)) return out;
   return write_int_noinline(out, make_write_int_arg(value, specs.sign), specs,
                             loc);
 }
@@ -2203,8 +2208,7 @@ template <typename Char, typename OutputIt, typename T,
 FMT_CONSTEXPR FMT_INLINE auto write(OutputIt out, T value,
                                     const basic_format_specs<Char>& specs,
                                     locale_ref loc) -> OutputIt {
-  if (specs.localized && write_loc(out, make_loc_value(value), specs, loc))
-    return out;
+  if (specs.localized && write_loc(out, value, specs, loc)) return out;
   return write_int(out, make_write_int_arg(value, specs.sign), specs, loc);
 }
 
@@ -3311,7 +3315,7 @@ FMT_CONSTEXPR20 auto write(OutputIt out, T value,
                            basic_format_specs<Char> specs, locale_ref loc = {})
     -> OutputIt {
   if (const_check(!is_supported_floating_point(value))) return out;
-  return specs.localized && write_loc(out, make_loc_value(value), specs, loc)
+  return specs.localized && write_loc(out, value, specs, loc)
              ? out
              : write_float(out, value, specs, loc);
 }

include/fmt/xchar.h

@@ -23,7 +23,7 @@ template <typename T>
 using is_exotic_char = bool_constant<!std::is_same<T, char>::value>;
 
 template <typename OutputIt>
-auto write_loc(OutputIt out, basic_format_arg<format_context> val,
+auto write_loc(OutputIt out, loc_value value,
                const basic_format_specs<wchar_t>& specs, locale_ref loc)
     -> bool {
 #ifndef FMT_STATIC_THOUSANDS_SEPARATOR
@@ -32,8 +32,7 @@ auto write_loc(OutputIt out, basic_format_arg<format_context> val,
   auto separator = std::wstring();
   auto grouping = numpunct.grouping();
   if (!grouping.empty()) separator = std::wstring(1, numpunct.thousands_sep());
-  return visit_format_arg(
-      loc_writer<wchar_t>{out, specs, separator, grouping, {}}, val);
+  return value.visit(loc_writer<wchar_t>{out, specs, separator, grouping, {}});
 #endif
   return false;
 }

test/format-test.cc

@@ -2335,14 +2335,13 @@ class format_facet : public fmt::format_facet<std::locale> {
     }
   };
 
-  auto do_put(fmt::appender out, fmt::basic_format_arg<fmt::format_context> arg,
+  auto do_put(fmt::appender out, fmt::loc_value val,
               const fmt::format_specs&) const -> bool override;
 };
 
-auto format_facet::do_put(fmt::appender out,
-                          fmt::basic_format_arg<fmt::format_context> arg,
+auto format_facet::do_put(fmt::appender out, fmt::loc_value val,
                           const fmt::format_specs&) const -> bool {
-  return visit_format_arg(int_formatter{out}, arg);
+  return val.visit(int_formatter{out});
 }
 
 TEST(format_test, format_facet) {