Can I make a type "sealed except for internal types"

Question

I want to make a type that can be inherited from by types in the same assembly, but cannot be inherited from outside of the assembly. I do want the type to be visible outside of the assembly.

Is this possible?

Answer 1

You can make the constructor internal:

public class MyClass
{
    internal MyClass() { }
}

Every class that derives from a base class must call a constructor of the base class in its constructor. Since it can't call the constructor if the base class is in a different assembly, the derived class doesn't compile.