The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License. Creative Commons License

// raw code

#include "color.hpp"
#include <iostream>
#include <string>
#include <format>

int main()
  for (auto val : {Color::red, Color::green, Color::blue, Color{13}}) {
    // use user-provided formatter for enum Color:
    std::cout << std::format("Color {:_>8} has value {:02}\n",
                             val, static_cast<int>(val));