Initializing a static constexpr from an incomplete type because of a template base class

Question

I have a template base class, whereby subclasses are expected to pass themselves as the template parameter.

It looks a little like this:

template<         


        

Answer 1

You can simply add constexpr to the definition of LIFE:

constexpr Derived Derived::LIFE = Derived(42);

Until recently GCC had a bug where it rejected this; you'll need to use either Clang or GCC 4.9.