Is it possible to forbid deriving from a class at compile time?

Question

I have a value class according to the description in \"C++ Coding Standards\", Item 32. In short, that means it provides value semantics and does not have any virtual method

Answer 1

I would generally achieve this as follows:

// This class is *not* suitable for use as a base class

The comment goes in the header and/or in the documentation. If clients of your class don't follow the instructions on the packet, then in C++ they can expect undefined behavior. Deriving without permission is just a special case of this. They should use composition instead.

Btw, this is slightly misleading: "a base class should have a destructor that is public and virtual or protected and nonvirtual".

That's true for classes which are to be used as bases for runtime polymorphism. But it's not necessary if derived classes are never going to be referenced via pointers to the base class type. It might be reasonable to have a value type which is used only for static polymorphism, for instance with simulated dynamic binding. The confusion is that inheritance can be used for different purposes in C++, requiring different support from the base class. It means that although you don't want dynamic polymorphism with your class, it might nevertheless be fine to create derived classes provided they're used correctly.