Compile time type determination in C++

Question

A coworker recently showed me some code that he found online. It appears to allow compile time determination of whether a type has an \"is a\" relationship with another type. I

Answer 1

Is there any reason you wouldn't use something like this instead:

template
struct IsRelated
{
    static DerivedT derived();
    static char test(const BaseT&); // sizeof(test()) == sizeof(char)
    static char (&test(...))[2];    // sizeof(test()) == sizeof(char[2])

    enum { exists = (sizeof(test(derived())) == sizeof(char)) }; 
}

?

e.g.:

IsRelated::exists

That way you have access to the information at compile-time.