CRTP compiling error

Question

The following will compile with GCC 5.2 but not with Visual Studio 2015.

template 
struct CRTP {
    static constexpr int num = Deriv         


        

Answer 1

Try making it a constexpr function instead. The way you have it setup now attempts to access an incomplete type.
Since a templated member function will only be initialized upon first being used, type A will be fully defined by that point.

#include 

template 
struct CRTP {
    static constexpr int num() { return  Derived::value + 1; }
};

struct A : CRTP {
    static constexpr int value = 5;
};

int main()
{
    std::cout << A::num();
    return 0;
}

See it live here