Blog idea!

sandbox.cc

#include <string>

template <auto Name>
struct Int { private: int n; };

struct EI : Int<1>, virtual Int<2> {};
struct DI : virtual Int<2> {};
struct FI : EI, DI {};

struct DC { int a1; int a2; };
struct EC { int a2; };
struct FC : EC, DC {};

int main() {
      FI x;
      (Int<2>)x; // Ok!

      FC y;
      y.a2; // Error!
}