text: #include <iostream>
  //#include <string_view>
  //#include <source_location>
   
  // void log(std::string_view message,
  //          const std::source_location& location = std::source_location::current())
  // {
  //     std::cout << "info:"
  //               << location.file_name() << ":"
  //               << location.line() << " "
  //               << message << '\n';
  // }
   
  int main()
  {
      std::cout << "Hello world!";
  //    log("Hello world!");  // info:main.cpp:15 Hello world!
      return 0;
  }
  
  