Static constexpr int vs old-fashioned enum: when and why?

Question

This is maybe a basic question, but I cannot see the response by myself right now.

Consider the following code:

template
struct T {
            


        

Answer 1

The currently accepted answer by SergeyA no longer holds as of C++17 (Definitions and ODR).

Every declaration is a definition, except for the following:

• ...
• (deprecated) Namespace scope declaration of a static data member that was defined within the class with the constexpr specifier

struct S {
    static constexpr int x = 42; // implicitly inline, defines S::x
};
constexpr int S::x; // declares S::x, not a redefinition

Hence, as of C++17, I would use the static constexpr definition which is more expressive than the enum.