Do not declare a member function template virtual

Reason

C++ does not support that. If it did, vtbls could not be generated until link time. And in general, implementations must deal with dynamic linking.

Example, don't

class Shape {
    // ...
    template<class T>
    virtual bool intersect(T* p);   // error: template cannot be virtual
};

Note

We need a rule because people keep asking about this

Alternative

Double dispatch, visitors, calculate which function to call

Enforcement

The compiler handles that.