Decouple locale and buffer

include/fmt/format.cc

@@ -220,9 +220,9 @@ void report_error(FormatFunc func, int error_code,
 }  // namespace
 
 template <typename Char>
-FMT_FUNC Char internal::thousands_sep(const basic_buffer<Char>& buf) {
+FMT_FUNC Char internal::thousands_sep(locale_provider *lp) {
-  return std::use_facet<std::numpunct<Char>>(buf.locale().get())
+  std::locale loc = lp ? lp->locale().get() : std::locale();
-                                            .thousands_sep();
+  return std::use_facet<std::numpunct<Char>>(loc).thousands_sep();
 }
 
 FMT_FUNC void system_error::init(
@@ -441,15 +441,15 @@ FMT_FUNC void vprint_colored(Color c, string_view format, format_args args) {
   std::fputs(RESET_COLOR, stdout);
 }
 
+FMT_FUNC locale locale_provider::locale() { return fmt::locale(); }
+
 #ifndef FMT_HEADER_ONLY
 
 template struct internal::basic_data<void>;
 
 // Explicit instantiations for char.
 
-template locale basic_buffer<char>::locale() const;
+template char internal::thousands_sep(locale_provider *lp);
-
-template char internal::thousands_sep(const basic_buffer<char>& buf);
 
 template void basic_fixed_buffer<char>::grow(std::size_t);
 
@@ -465,9 +465,7 @@ template int internal::char_traits<char>::format_float(
 
 // Explicit instantiations for wchar_t.
 
-template locale basic_buffer<wchar_t>::locale() const;
+template wchar_t internal::thousands_sep(locale_provider *lp);
-
-template wchar_t internal::thousands_sep(const basic_buffer<wchar_t>& buf);
 
 template class basic_context<wchar_t>;
 

include/fmt/format.h

@@ -305,11 +305,13 @@ inline T *make_ptr(T *ptr, std::size_t) { return ptr; }
 // is very heavy.
 class locale;
 
-/**
+class locale_provider {
-  \rst
+ public:
-  A contiguous memory buffer with an optional growing ability.
+  virtual ~locale_provider() {}
-  \endrst
+  virtual locale locale();
- */
+};
+
+/** A contiguous memory buffer with an optional growing ability. */
 template <typename T>
 class basic_buffer {
  private:
@@ -381,8 +383,6 @@ class basic_buffer {
 
   T &operator[](std::size_t index) { return ptr_[index]; }
   const T &operator[](std::size_t index) const { return ptr_[index]; }
-
-  virtual fmt::locale locale() const;
 };
 
 template <typename T>
@@ -868,7 +868,7 @@ class add_thousands_sep {
 };
 
 template <typename Char>
-Char thousands_sep(const basic_buffer<Char>& buf);
+Char thousands_sep(locale_provider *lp);
 
 // Formats a decimal unsigned integer value writing into buffer.
 // thousands_sep is a functor that is called after writing each char to
@@ -2182,6 +2182,7 @@ class basic_writer {
  private:
   // Output buffer.
   Buffer &buffer_;
+  std::unique_ptr<locale_provider> locale_;
 
   FMT_DISALLOW_COPY_AND_ASSIGN(basic_writer);
 
@@ -2591,7 +2592,8 @@ void basic_writer<Buffer>::write_int(T value, const Spec& spec) {
 
     void on_num() {
       unsigned num_digits = internal::count_digits(abs_value);
-      char_type thousands_sep = internal::thousands_sep(writer.buffer_);
+      char_type thousands_sep =
+          internal::thousands_sep<char_type>(writer.locale_.get());
       fmt::basic_string_view<char_type> sep(&thousands_sep, 1);
       unsigned size = static_cast<unsigned>(
             num_digits + sep.size() * ((num_digits - 1) / 3));

include/fmt/locale.h

@@ -19,7 +19,4 @@ class locale {
   explicit locale(std::locale loc = std::locale()) : locale_(loc) {}
   std::locale get() { return locale_; }
 };
-
-template <typename T>
-locale basic_buffer<T>::locale() const { return fmt::locale(); }
 }