A c++11 metafunction to check if a class has a method

has_method_def.h

// Create a metafunction "has_xxx_method" that can be used
// to check if a class has a method called "xxx". Note the
// limitation: only existence of parameterless methods can
// be checked this way.
// Credits: http://stackoverflow.com/a/21827727/1525865
#define HAS_METHOD_DEF(xxx)                              \
  template<typename T>                                   \
  constexpr auto has_ ## xxx ## _method(int)             \
  -> decltype(std::declval<T>(). xxx (), bool())         \
  { return true; }                                       \
  template<typename T>                                   \
  constexpr bool has_ ## xxx ## _method(...)             \
  { return false; }