willcool4ever • 模版检查类中是否有某个成员函数

//例子1
template<typename T>
struct has_no_destroy
{
  template <typename C> static char test(decltype(&C::no_destroy));
  template <typename C> static int32_t test(...);
  const static bool value = sizeof(test<T>(0)) == 1;
};

//例子2

template<typename T, typename Sig>
struct has_foo {
    template <typename U, U> struct type_check;
    template <typename V> static char (& chk(type_check<Sig, &V::foo>*))[1];
    template <typename  > static char (& chk(...))[2];
    static bool const value = (sizeof(chk<T>(0)) == 1);
};

template <typename Type>
class has_foo
{
   class yes { char m;};
   class no { yes m[2];};
   struct BaseMixin
   {
     void foo(){}
   };
   struct Base : public Type, public BaseMixin {};
   template <typename T, T t>  class Helper{};
   template <typename U>
   static no deduce(U*, Helper<void (BaseMixin::*)(), &U::foo>* = 0);
   static yes deduce(...);
public:
   static const bool result = sizeof(yes) == sizeof(deduce((Base*)(0)));
};