Curiously recurring template pattern (CRTP) with static constexpr in Clang

Question

Consider my simple example below:

#include 

template 
class Base
{
public:
    static constexpr int y = T::x;
};

class Derive         


        

Answer 1

As linked in the comments, Initializing a static constexpr data member of the base class by using a static constexpr data member of the derived class suggests that clang behaviour is standard conformant up to C++14 here. Starting with Clang 3.9, your code compiles successfully with -std=c++1z. An easy possible workaround is to use constexpr functions instead of values:

#include 

template 
class Base
{
public:
    static constexpr int y() {return T::x();}
};

class Derived : public Base
{
public:
    static constexpr int x() {return 5;}
};

int main()
{
    std::cout << Derived::y() << std::endl;
}