小编Hsu*_*Hau的帖子

我想ostream&通过查看是否提供了重载来测试类是否可以流式传输operator<<.根据这些 帖子,我尝试使用C++ 11编写另一个版本.这是我的尝试:

#include <iostream>
#include <type_traits>

namespace TEST{
  class NotDefined{};

  template<typename T> 
  NotDefined& operator << (::std::ostream&, const T&);

  template <typename T>
  struct StreamInsertionExists {
    static std::ostream &s;
    static T const &t;
    enum { value = std::is_same<decltype(s << t), NotDefined>() };
  };
}

struct A{
  int val;
    friend ::std::ostream& operator<<(::std::ostream&, const A&);
};

::std::ostream& operator<<(::std::ostream& os, const A& a)
{
  os << a.val;
  return os;
}

struct B{};

int main() {
  std::cout << TEST::StreamInsertionExists<A>::value …