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

The original code will construct an object of Derived, it may brings unexpected result. Below work may be an alternative choice:

template
inline  bool    isDerived(const CheckT &t){
    char    test(const BaseT   *t);
    char    (&test(...))[2];
    return  (sizeof(test(&t)) == sizeof(char) );
}