Method operator=

include/fmt/format.h:2259–2265

      return *this;
    }
    FMT_CONSTEXPR auto operator=(char c) -> bounded_output_iterator& {
      if (bound > 0) {
        *underlying_iterator++ = c;
        --bound;
      }
      return *this;
    }
  };

  return write_padded<char>(