Checking whether a function (not a method) exists in c++11 via templates

Question

So with SFINAE and c++11, it is possible to implement two different template functions based on whether one of the template parameters can be substituted.

For exampl

Answer 1

Using SFINAE, it's possible like this:

template 
class has_ostream_lshift
{
  struct no {};

  template 
  static decltype(std::declval() << std::declval()) test(int);

  template 
  static no test(...);

public:
  enum { value = ! std::is_same(0))>::value};
};