SFINAE compiler troubles

Question

The following code of mine should detect whether T has begin and end methods:

template 
struct is_contai         


        

Answer 1

With C++11, there are now better ways to detect this. Instead of relying on the signature of functions, we simply call them in an expression SFINAE context:

#include  // declval

template
class is_container{
  typedef char (&two)[2];

  template // non-const
  static auto test(typename U::iterator*, int)
      -> decltype(std::declval().begin(), char());

  template // const
  static auto test(typename U::const_iterator*, long)
      -> decltype(std::declval().begin(), char());

  template
  static two  test(...);

public:
  static bool const value = sizeof(test(0, 0)) == 1;
};

Live example on Ideone. The int and long parameters are only to disambiguate overload resolution when the container offers both (or if iterator is typedef const_iterator iterator, like std::set is allowed to) - literal 0 is of type int and forces the first overload to be chosen.