如何实现std :: experimental :: source_location？

库基础知识的C++扩展,版本2(N4564)介绍了该类型std::experimental::source_location.

§14.1.2[reflection.src_loc.creation]说:

static constexpr source_location current() noexcept;

返回:当函数调用(C++14§5.2.2)调用其后缀表达式(可能是带括号的)id-expression命名时current,返回source_location带有实现定义值的a.该值应受#line(C++14§16.4)影响,其方式与__LINE__和__FILE__.如果以其他方式调用,则返回的值未指定.

备注:当使用大括号或等于初始化程序来初始化非静态数据成员时,任何调用都current应该对应于构造函数的位置或初始化成员的聚合初始化.

[ 注意:当用作默认参数(C++14§8.3.6)时,该值source_location将是current呼叫站点呼叫的位置.- 结束说明 ]

如果我理解正确,那么该功能就像这样使用.

#include   // I don't actually have this header
#include 
#include 
#include 

struct my_exception
{

  std::string message {};
  std::experimental::source_location location {};

  my_exception(std::string msg,
               std::experimental::source_location loc = std::experimental::source_location::current()) :
    message {std::move(msg)},
    location {std::move(loc)}
  {
  }

};

int
do_stuff(const int a, const int b)
{
  if (a > b)
    throw my_exception {"a > b"};  // line 25 of file main.cxx
  return b - a;
}

int
main()
{
  try
    {
      std::cout << do_stuff(2, 1) << "\n";
    }
  catch (const my_exception& e)
    {
      std::cerr << e.location.file_name() << ":" << e.location.line() << ": "
                << "error: " << e.message << "\n";
    }
}

main.cxx:25: error: a > b