Static claim to check static const class?

Yes, static_assert()you can place it anywhere an ad can appear. This includes the class body:

class C {
public:
    enum E {
      A, B, C,
      NumEes
    };
    constexpr Foo foos[] = { {...}, {...}, {...} };
    static_assert( NumEes == sizeof foos / sizeof *foos, "size mismatch" );

    // ...
};