SFINAE works differently in cases of type and non-type template parameters

Question

Why does this code work:

template<
    typename T, 
    std::enable_if_t::value, T>* = nullptr>
void Add(T) {}

templa         


        

Answer 1

I think the problem is the fact that you can use a function even if a default template parameter does not compile by specifying a different value for it. Think of what would happen if you specified two template parameters in a call to add.