Method write_padded

extlibs/fmt/include/fmt/format.h:1677–1698

  //   <left-padding><value><right-padding>
  // where <value> is written by f(it).
  template <typename F> void write_padded(const format_specs& specs, F&& f) {
    // User-perceived width (in code points).
    unsigned width = to_unsigned(specs.width);
    size_t size = f.size();  // The number of code units.
    size_t num_code_points = width != 0 ? f.width() : size;
    if (width <= num_code_points) return f(reserve(size));
    size_t padding = width - num_code_points;
    size_t fill_size = specs.fill.size();
    auto&& it = reserve(size + padding * fill_size);
    if (specs.align == align::right) {
      it = fill(it, padding, specs.fill);
      f(it);
    } else if (specs.align == align::center) {
      std::size_t left_padding = padding / 2;
      it = fill(it, left_padding, specs.fill);
      f(it);
      it = fill(it, padding - left_padding, specs.fill);
    } else {
      f(it);
      it = fill(it, padding, specs.fill);
    }
  }

  void write(int value) { write_decimal(value); }
  void write(long value) { write_decimal(value); }