How to write `is_complete` template?

Question

After answering this question I was trying to find is_complete template in Boost library and I realized that there is no such template in Boost.TypeTraits. Why

Answer 1

template
struct is_complete {
    static T & getT();
    static char (& pass(T))[2];
    static char pass(...);

    static const bool value = sizeof(pass(getT()))==2;
};