Visibility of nester class constructor

Question

Is there a way to limit the instantiation of the nested class in C#? I want to prevent nested class being instantiated from any other class except the nesting class, but to allow full access to the nested class from other code.

Answer 1

Usually I create an interface for the functionality you want to expose to other classes, then make the nested class private and implement that interface. This way the nested class definition can stay hidden:

public class Outer
{
    private class Nested : IFace
    {
        public Nested(...)
        {
        }
        //interface member implementations...
    }

    public IFace GetNested()
    {
        return new Nested();
    }
}

Answer 2

In short, no, you cannot do that. There is an accessibity modifier "public" which means "accessible by anything inside me or outside me" and there is an accessibility modifier "private" which means "accessible by anything inside me". There is no modifier which means "accessible to the thing immediately outside me but not to anything outside it", which is what you would need to mark the constructor as. That's simply not a concept that the designers of the type system thought would be useful.

Can you describe why you want this crazy kind of accessibility? Perhaps there is a better way to get what you want.