🎉 Array overload safety for base.h only

include/fmt/base.h

@@ -259,6 +259,8 @@
 #  define FMT_UNICODE !FMT_MSC_VERSION
 #endif
 
+#define FMT_FWD(...) static_cast<decltype(__VA_ARGS__)&&>(__VA_ARGS__)
+
 // Enable minimal optimizations for more compact code in debug mode.
 FMT_GCC_PRAGMA("GCC push_options")
 #if !defined(__OPTIMIZE__) && !defined(__CUDACC__)
@@ -2809,15 +2811,43 @@ using format_string = basic_format_string<char, type_identity_t<Args>...>;
 inline auto runtime(string_view s) -> runtime_format_string<> { return {{s}}; }
 #endif
 
+template <typename... Args>
+using format_string = basic_format_string<char, type_identity_t<Args>...>;
 /** Formats a string and writes the output to ``out``. */
 template <typename OutputIt,
-          FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char>::value)>
-auto vformat_to(OutputIt out, string_view fmt, format_args args) -> OutputIt {
+          FMT_ENABLE_IF(detail::is_output_iterator<remove_cvref_t<OutputIt>,
+                                                   char>::value)>
+auto vformat_to(OutputIt&& out, string_view fmt, format_args args)
+    -> remove_cvref_t<OutputIt> {
   auto&& buf = detail::get_buffer<char>(out);
   detail::vformat_to(buf, fmt, args, {});
   return detail::get_iterator(buf, out);
 }
 
+template <typename OutputIt, typename OutputSen = OutputIt>
+struct format_to_result {
+  /** Iterator past the end of the last write. */
+  OutputIt out;
+  /** Iterator to the end of the output range. */
+  OutputSen out_last;
+
+  FMT_CONSTEXPR operator OutputIt&() & noexcept { return out; }
+  FMT_CONSTEXPR operator const OutputIt&() const& noexcept { return out; }
+  FMT_CONSTEXPR operator OutputIt&&() && noexcept {
+    return static_cast<OutputIt&&>(out);
+  }
+};
+
+/** Formats a string and writes the output to ``out``. */
+template <size_t Size>
+auto vformat_to(char (&out)[Size], string_view fmt, format_args args)
+    -> format_to_result<char*> {
+  using traits = detail::fixed_buffer_traits;
+  auto buf = detail::iterator_buffer<char*, char, traits>(out, Size);
+  detail::vformat_to(buf, fmt, args, {});
+  return {out + buf.count(), out + Size};
+}
+
 /**
  \rst
  Formats ``args`` according to specifications in ``fmt``, writes the result to
@@ -2831,9 +2861,28 @@ auto vformat_to(OutputIt out, string_view fmt, format_args args) -> OutputIt {
  \endrst
  */
 template <typename OutputIt, typename... T,
-          FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char>::value)>
-FMT_INLINE auto format_to(OutputIt out, format_string<T...> fmt, T&&... args)
-    -> OutputIt {
+          FMT_ENABLE_IF(detail::is_output_iterator<remove_cvref_t<OutputIt>,
+                                                   char>::value)>
+FMT_INLINE auto format_to(OutputIt&& out, format_string<T...> fmt, T&&... args)
+    -> remove_cvref_t<OutputIt> {
+  return vformat_to(FMT_FWD(out), fmt, fmt::make_format_args(args...));
+}
+
+/**
+ \rst
+ Formats ``args`` according to specifications in ``fmt``, writes the result to
+ the output iterator ``out`` and returns the iterator past the end of the output
+ range. `format_to` does not append a terminating null character.
+
+ **Example**::
+
+   auto out = std::vector<char>();
+   fmt::format_to(std::back_inserter(out), "{}", 42);
+ \endrst
+ */
+template <size_t Size, typename... T>
+FMT_INLINE auto format_to(char (&out)[Size], format_string<T...> fmt,
+                          T&&... args) -> format_to_result<char*> {
   return vformat_to(out, fmt, fmt::make_format_args(args...));
 }