//********************************************************
// The following code example is taken from the book
//  C++20 - The Complete Guide
//  by Nicolai M. Josuttis (www.josuttis.com)
//  http://www.cppstd20.com
//
// The code is licensed under a
//  Creative Commons Attribution 4.0 International License
//  http://creativecommons.org/licenses/by/4.0/
//********************************************************


#include <iostream>
#include <string_view>

template<auto Prefix>
class Logger {
  //...
 public:
  void log(std::string_view msg) const {
    std::cout << Prefix << msg << '\n';
  }
};

template<std::size_t N>
struct Str {
  char chars[N];
  const char* value() {
    return chars;
  }
  friend std::ostream& operator<< (std::ostream& strm, const Str& s) {
    return strm << s.chars;
  }
};
template<std::size_t N> Str(const char(&)[N]) -> Str<N>;  // deduction guide

int main()
{
  Logger<Str{"> "}> logger;
  logger.log("hello");
}