How can I create a class A in C#, where A can only be inherited by B, C, D?

Question

There is some mechanism to allow a class to be inherited by N classes only in C#?

Answer 1

You may put it and it's derived classes in a separate assembly, and declare the constructor of the base class as internal. That way although you could inherit from it in a different assembly, but you wouldn't be able to instantiate any derived class.

Answer 2

No, but you can always make the constructor throw an exception if it exceeds the limit.

Answer 3

// can be inherited only by classes in the same assembly
public abstract class A
{
    protected internal A() { }
}

// can't be inherited
public sealed class B : A
{
}