Improve handling of thousands separator

include/fmt/format-inl.h

@@ -103,23 +103,18 @@ template <typename Locale> Locale locale_ref::get() const {
   return locale_ ? *static_cast<const std::locale*>(locale_) : std::locale();
 }
 
-template <typename Char> FMT_FUNC std::string grouping_impl(locale_ref loc) {
-  return std::use_facet<std::numpunct<Char>>(loc.get<std::locale>()).grouping();
-}
-template <typename Char> FMT_FUNC Char thousands_sep_impl(locale_ref loc) {
-  return std::use_facet<std::numpunct<Char>>(loc.get<std::locale>())
-      .thousands_sep();
+template <typename Char>
+FMT_FUNC auto thousands_sep_impl(locale_ref loc) -> thousands_sep_result<Char> {
+  auto& facet = std::use_facet<std::numpunct<Char>>(loc.get<std::locale>());
+  return {facet.grouping(), facet.thousands_sep()};
 }
 template <typename Char> FMT_FUNC Char decimal_point_impl(locale_ref loc) {
   return std::use_facet<std::numpunct<Char>>(loc.get<std::locale>())
       .decimal_point();
 }
 #else
-template <typename Char> FMT_FUNC std::string grouping_impl(locale_ref) {
-  return "\03";
-}
 template <typename Char> FMT_FUNC Char thousands_sep_impl(locale_ref) {
-  return FMT_STATIC_THOUSANDS_SEPARATOR;
+  return {"\03", FMT_STATIC_THOUSANDS_SEPARATOR};
 }
 template <typename Char> FMT_FUNC Char decimal_point_impl(locale_ref) {
   return '.';

include/fmt/format.h

@@ -1015,22 +1015,20 @@ template <> constexpr auto digits10<uint128_t>() FMT_NOEXCEPT -> int {
   return 38;
 }
 
-// DEPRECATED! grouping will be merged into thousands_sep.
-template <typename Char>
-FMT_API auto grouping_impl(locale_ref loc) -> std::string;
-template <typename Char> inline auto grouping(locale_ref loc) -> std::string {
-  return grouping_impl<char>(loc);
-}
-template <> inline auto grouping<wchar_t>(locale_ref loc) -> std::string {
-  return grouping_impl<wchar_t>(loc);
-}
+template <typename Char> struct thousands_sep_result {
+  std::string grouping;
+  Char thousands_sep;
+};
 
 template <typename Char>
-FMT_API auto thousands_sep_impl(locale_ref loc) -> Char;
-template <typename Char> inline auto thousands_sep(locale_ref loc) -> Char {
-  return Char(thousands_sep_impl<char>(loc));
+FMT_API auto thousands_sep_impl(locale_ref loc) -> thousands_sep_result<Char>;
+template <typename Char>
+inline auto thousands_sep(locale_ref loc) -> thousands_sep_result<Char> {
+  auto result = thousands_sep_impl<char>(loc);
+  return {result.grouping, Char(result.thousands_sep)};
 }
-template <> inline auto thousands_sep(locale_ref loc) -> wchar_t {
+template <>
+inline auto thousands_sep(locale_ref loc) -> thousands_sep_result<wchar_t> {
   return thousands_sep_impl<wchar_t>(loc);
 }
 
@@ -1419,10 +1417,10 @@ auto write_int_localized(OutputIt& out, UInt value, unsigned prefix,
     -> bool {
   static_assert(std::is_same<uint64_or_128_t<UInt>, UInt>::value, "");
   const auto sep_size = 1;
-  std::string groups = grouping<Char>(loc);
-  if (groups.empty()) return false;
-  auto sep = thousands_sep<Char>(loc);
-  if (!sep) return false;
+  auto ts = thousands_sep<Char>(loc);
+  const std::string& groups = ts.grouping;
+  Char sep = ts.thousands_sep;
+  if (!sep || groups.empty()) return false;
   int num_digits = count_digits(value);
   int size = num_digits, n = num_digits;
   std::string::const_iterator group = groups.cbegin();
@@ -2736,10 +2734,10 @@ extern template void vformat_to(detail::buffer<char>&, string_view,
                                 basic_format_args<format_context>,
                                 detail::locale_ref);
 
-extern template FMT_API auto grouping_impl<char>(locale_ref) -> std::string;
-extern template FMT_API auto grouping_impl<wchar_t>(locale_ref) -> std::string;
-extern template FMT_API auto thousands_sep_impl<char>(locale_ref) -> char;
-extern template FMT_API auto thousands_sep_impl<wchar_t>(locale_ref) -> wchar_t;
+extern template FMT_API auto thousands_sep_impl<char>(locale_ref)
+    -> thousands_sep_result<char>;
+extern template FMT_API auto thousands_sep_impl<wchar_t>(locale_ref)
+    -> thousands_sep_result<wchar_t>;
 extern template FMT_API auto decimal_point_impl(locale_ref) -> char;
 extern template FMT_API auto decimal_point_impl(locale_ref) -> wchar_t;
 extern template auto format_float<double>(double value, int precision,

src/format.cc

@@ -41,8 +41,8 @@ template FMT_API std::locale detail::locale_ref::get<std::locale>() const;
 
 // Explicit instantiations for char.
 
-template FMT_API std::string detail::grouping_impl<char>(locale_ref);
-template FMT_API char detail::thousands_sep_impl(locale_ref);
+template FMT_API auto detail::thousands_sep_impl(locale_ref)
+    -> thousands_sep_result<char>;
 template FMT_API char detail::decimal_point_impl(locale_ref);
 
 template FMT_API void detail::buffer<char>::append(const char*, const char*);
@@ -63,8 +63,8 @@ template FMT_API int detail::format_float(long double, int, detail::float_specs,
 
 // Explicit instantiations for wchar_t.
 
-template FMT_API std::string detail::grouping_impl<wchar_t>(locale_ref);
-template FMT_API wchar_t detail::thousands_sep_impl(locale_ref);
+template FMT_API auto detail::thousands_sep_impl(locale_ref)
+    -> thousands_sep_result<wchar_t>;
 template FMT_API wchar_t detail::decimal_point_impl(locale_ref);
 
 template FMT_API void detail::buffer<wchar_t>::append(const wchar_t*,