这个代码真的是绝了
typedef char (&yes)[1];
typedef char (&no)[2];
template <typename B, typename D>
struct Host
{
operator B*() const;
operator D*();
};
template <typename B, typename D>
struct is_base_of
{
template <typename T>
static yes check(D*, T);
static no check(B*, int);
static const bool value = sizeof(check(Host<B,D>(), int())) == sizeof(yes);
};