Question

I have a base class and several subclasses derived from that base class. I also have a static function in the base class that takes some parameters, and instantiates and returns an appropriate subclass based on input parameters ( my factory method.)

Now here’s my problem: I want to ONLY allow instantiation of the subclasses FROM the factory method. But if I set the constructors of the subclasses to be protected, the base class can’t see them. Is there an access modifier I’m missing that would allow the base class to call the subclasses constructors, but not not allow any other classes to call them?

Internal doesn’t look like it will work either…I want to limit access to the subclass constructors to just the base class, there are other classes in the same assembly that should be able to access the base factory method and but not directly instantiate any of the subclasses.

Hopefully there’s something really simple I’m missing…

Example:

public class Base
{
    public Base CreateChild(string childType)
    {
        if(childType == "A")
            return new ChildA();
        if(childType == "B")
            return new ChildB();

        return null;
    }
}

public class ChildA
{
    protected ChildA() // This doesn't work, since now base class can't call this!
    {
    }
}

public class ChildB
{
    protected ChildB()
    {
    }
}

Answer 1

You can declare the child classes as private nested classes inside Base