How `is_base_of` works?
- by Alexey Malistov
Why the following code works?
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);
};
//Test sample
class Base {};
class Derived : private Base {};
//Exspression is true.
int test[is_base_of<Base,Derived>::value && !is_base_of<Derived,Base>::value];
Note that B is private base. Note that operator B*() is const.
How does this work? Why this works?
Why static yes check(D*, T); is better than static yes check(B*, int); ?
