Implement format_facet

include/fmt/format.h

@@ -988,17 +988,23 @@ constexpr auto compile_string_to_view(detail::std_string_view<Char> s)
 // 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 {
+ private:
+  std::string separator_;
+
+ protected:
+  virtual void do_put(appender out, basic_format_arg<format_context> val,
+                      const format_specs& specs, Locale& loc) const;
+
  public:
   static FMT_API typename Locale::id id;
 
+  explicit format_facet(string_view sep = ",")
+      : separator_(sep.data(), sep.size()) {}
+
   void put(appender out, basic_format_arg<format_context> val,
            const format_specs& specs, Locale& loc) const {
     do_put(out, val, specs, loc);
   }
-
- protected:
-  virtual void do_put(appender out, basic_format_arg<format_context> val,
-                      const format_specs& specs, Locale& loc) const = 0;
 };
 
 FMT_BEGIN_DETAIL_NAMESPACE
@@ -1949,19 +1955,19 @@ FMT_CONSTEXPR FMT_INLINE auto write_int(OutputIt out, int num_digits,
 
 template <typename Char> class digit_grouping {
  private:
-  thousands_sep_result<Char> sep_;
+  std::string grouping_;
+  std::basic_string<Char> thousands_sep_;
 
   struct next_state {
     std::string::const_iterator group;
     int pos;
   };
-  next_state initial_state() const { return {sep_.grouping.begin(), 0}; }
+  next_state initial_state() const { return {grouping_.begin(), 0}; }
 
   // Returns the next digit group separator position.
   int next(next_state& state) const {
-    if (!sep_.thousands_sep) return max_value<int>();
-    if (state.group == sep_.grouping.end())
-      return state.pos += sep_.grouping.back();
+    if (thousands_sep_.empty()) return max_value<int>();
+    if (state.group == grouping_.end()) return state.pos += grouping_.back();
     if (*state.group <= 0 || *state.group == max_value<char>())
       return max_value<int>();
     state.pos += *state.group++;
@@ -1970,14 +1976,16 @@ template <typename Char> class digit_grouping {
 
  public:
   explicit digit_grouping(locale_ref loc, bool localized = true) {
-    if (localized)
-      sep_ = thousands_sep<Char>(loc);
-    else
-      sep_.thousands_sep = Char();
+    if (!localized) return;
+    auto sep = thousands_sep<Char>(loc);
+    grouping_ = sep.grouping;
+    if (sep.thousands_sep) thousands_sep_.assign(1, sep.thousands_sep);
   }
-  explicit digit_grouping(thousands_sep_result<Char> sep) : sep_(sep) {}
+  explicit digit_grouping(thousands_sep_result<Char> sep)
+      : grouping_(sep.grouping),
+        thousands_sep_(sep.thousands_sep ? 1 : 0, sep.thousands_sep) {}
 
-  Char separator() const { return sep_.thousands_sep; }
+  bool has_separator() const { return !thousands_sep_.empty(); }
 
   int count_separators(int num_digits) const {
     int count = 0;
@@ -2000,7 +2008,9 @@ template <typename Char> class digit_grouping {
     for (int i = 0, sep_index = static_cast<int>(separators.size() - 1);
          i < num_digits; ++i) {
       if (num_digits - i == separators[sep_index]) {
-        *out++ = separator();
+        out =
+            copy_str<Char>(thousands_sep_.data(),
+                           thousands_sep_.data() + thousands_sep_.size(), out);
         --sep_index;
       }
       *out++ = static_cast<Char>(digits[to_unsigned(i)]);
@@ -2307,7 +2317,7 @@ template <typename Char, typename OutputIt, typename T, typename Grouping>
 FMT_CONSTEXPR20 auto write_significand(OutputIt out, T significand,
                                        int significand_size, int exponent,
                                        const Grouping& grouping) -> OutputIt {
-  if (!grouping.separator()) {
+  if (!grouping.has_separator()) {
     out = write_significand<Char>(out, significand, significand_size);
     return detail::fill_n(out, exponent, static_cast<Char>('0'));
   }
@@ -2369,7 +2379,7 @@ FMT_CONSTEXPR20 auto write_significand(OutputIt out, T significand,
                                        int significand_size, int integral_size,
                                        Char decimal_point,
                                        const Grouping& grouping) -> OutputIt {
-  if (!grouping.separator()) {
+  if (!grouping.has_separator()) {
     return write_significand(out, significand, significand_size, integral_size,
                              decimal_point);
   }
@@ -2492,7 +2502,7 @@ template <typename Char> class fallback_digit_grouping {
  public:
   constexpr fallback_digit_grouping(locale_ref, bool) {}
 
-  constexpr Char separator() const { return Char(); }
+  constexpr bool has_separator() const { return false; }
 
   constexpr int count_separators(int) const { return 0; }