How can I define a template class which gives the pointer depth/level of a type?

Question

How can I define a template class which provides an integer constant representing the "depth" of a (pointer) type provided as the input template argument? For example, if the class was called Depth, the following would be true:

Depth<int ***>::value == 3
Depth<int>::value == 0

Answer 1

template <typename T> 
struct pointer_depth_impl
{
    enum { value = 0 };
};

template <typename T>
struct pointer_depth_impl<T* const volatile>
{
    enum { value = pointer_depth_impl<T const volatile>::value + 1 };
};

template <typename T>
struct pointer_depth
{
    enum { value = pointer_depth_impl<T const volatile>::value };
};