実装例を追加

Author: tetsurom

reference/format/format_to_n.md

@@ -111,6 +111,74 @@ int main()
 The answer is 42.
 ```
 
+
+## 実装例
+
+```cpp
+template<class CharT, class Out>
+class Wrapper {
+  std::iter_difference_t<Out> count_ = 0;
+  std::iter_difference_t<Out> max_count_;
+  Out out_;
+  
+public:
+  using value_type = CharT;
+
+  Wrapper(Out out, std::iter_difference_t<Out> max_count)
+    : max_count_(max_count)
+    , out_(std::move(out))
+  {}
+
+  constexpr void push_back(const value_type& value) {
+    if (count_ < max_count_) {
+      *out_ = value;
+      ++out_;
+    }
+    ++count_;
+  }
+
+  constexpr std::format_to_n_result<Out> result() const {
+    return {out_, count_};
+  }
+};
+
+template<class Out, class... Args>
+format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, format_string<Args...> fmt, Args&&... args) {
+  Wrapper<char, Out> wrapper(out, n);
+  format_to(back_inserter(wrapper), fmt, forward<Args>(args)...);
+  return wrapper.result();
+}
+
+template<class Out, class... Args>
+format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, wformat_string<Args...> fmt, Args&&... args) {
+  Wrapper<wchar_t, Out> wrapper(out, n);
+  format_to(back_inserter(wrapper), fmt, forward<Args>(args)...);
+  return wrapper.result();
+}
+
+template<class Out, class... Args>
+format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, const locale& loc, format_string<Args...> fmt, Args&&... args) {
+  Wrapper<char, Out> wrapper(out, n);
+  format_to(back_inserter(wrapper), loc, fmt, forward<Args>(args)...);
+  return wrapper.result();
+}
+
+template<class Out, class... Args>
+format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n, const locale& loc, wformat_string<Args...> fmt, Args&&... args) {
+  Wrapper<wchar_t, Out> wrapper(out, n);
+  format_to(back_inserter(wrapper), loc, fmt, forward<Args>(args)...);
+  return wrapper.result();
+}
+```
+* format_string[link basic_format_string.md]
+* wformat_string[link basic_format_string.md]
+* format_to[link format_to.md]
+* locale[link /reference/locale/locale.md]
+* forward[link /reference/utility/forward.md]
+* back_inserter[link /reference/iterator/back_inserter.md]
+* iter_difference_t[link /reference/iterator/iter_difference_t.md]
+
+
 ## バージョン
 ### 言語
 - C++20

reference/format/formatted_size.md

@@ -78,6 +78,59 @@ int main()
 17
 ```
 
+## 実装例
+
+```cpp
+template<class CharT>
+class Counter {
+  size_t count_ = 0;
+public:
+  using value_type = CharT;
+
+  constexpr void push_back(const value_type&) {
+    count_++;
+  }
+
+  constexpr size_t size() const {
+    return count_;
+  }
+};
+
+template<class Out, class... Args>
+size_t formatted_size(format_string<Args...> fmt, const Args&... args) {
+  Counter<char> counter;
+  format_to(back_inserter(counter), fmt, forward<Args>(args)...);
+  return counter.size();
+}
+
+template<class Out, class... Args>
+size_t formatted_size(wformat_string<Args...> fmt, const Args&... args) {
+  Counter<wchar_t> counter;
+  format_to(back_inserter(counter), fmt, forward<Args>(args)...);
+  return counter.size();
+}
+
+template<class Out, class... Args>
+size_t formatted_size(const locale& loc, format_string<Args...> fmt, const Args&... args) {
+  Counter<char> counter;
+  format_to(loc, back_inserter(counter), fmt, forward<Args>(args)...);
+  return counter.size();
+}
+
+template<class Out, class... Args>
+size_t formatted_size(const locale& loc, wformat_string<Args...> fmt, const Args&... args) {
+  Counter<wchar_t> counter;
+  format_to(loc, back_inserter(counter), fmt, forward<Args>(args)...);
+  return counter.size();
+}
+```
+* format_string[link basic_format_string.md]
+* wformat_string[link basic_format_string.md]
+* format_to[link format_to.md]
+* locale[link /reference/locale/locale.md]
+* forward[link /reference/utility/forward.md]
+* back_inserter[link /reference/iterator/back_inserter.md]
+
 ## バージョン
 ### 言語
 - C++20

reference/format/vformat.md

@@ -44,6 +44,43 @@ namespace std {
 
 フォーマット実行時に失敗した場合、[`format_error`](format_error.md)を投げる。
 
+## 実装例
+
+```cpp
+string vformat(string_view fmt, format_args args) {
+  string str;
+  vformat_to(back_inserter(str), fmt.str, args);
+  return str;
+}
+
+string vformat(wstring_view fmt, wformat_args args) {
+  wstring str;
+  vformat_to(back_inserter(str), fmt.str, args);
+  return str;
+}
+
+string vformat(const locale& loc, string_view fmt, format_args args) {
+  string str;
+  vformat_to(loc, back_inserter(str), fmt.str, args);
+  return str;
+}
+
+string vformat(const locale& loc, wstring_view fmt, wformat_args args) {
+  wstring str;
+  vformat_to(loc, back_inserter(str), fmt.str, args);
+  return str;
+}
+```
+* string[link /reference/string/basic_string.md]
+* wstring[link /reference/string/basic_string.md]
+* string_view[link /reference/string_view/basic_string_view.md]
+* wstring_view[link /reference/string_view/basic_string_view.md]
+* format_args[link /reference/format/basic_format_args.md]
+* wformat_args[link /reference/format/basic_format_args.md]
+* locale[link /reference/locale/locale.md]
+* vformat_to[link vformat.md]
+* back_inserter[link /reference/iterator/back_inserter.md]
+
 ## バージョン
 ### 言語
 - C++20