Question

I have a class with some child (inner, not derived) classes. Ideally, I’d like some fields of the child classes to be modifiable by the parent, but not be public. Is there a design in C# that accomplishes this? I can think of no way to use the typical access modifiers (protected, private, public, etc)

For example, imagine

Class Car{
    private Wheel wheel;
    Class Wheel
    {
        //I want this to be only accessible within Car and Wheel
        private int wheelSize;
    }
}

So, That’s not my real code, but conveys the idea of what I want to do just fine.

Answer 1

You could derive a private inner class from Wheel that has additional public members. The Wheel class would be abstract. this ensures that no instance of it can be created. Create a static method that creates wheels. The method would create a PrivateWheel but return it as Wheel. Wheels would always be exposed as Wheel but efectively be of type PrivateWheel.

public class Car {

    private PrivateWheel wheel;

    public Wheel { get { return wheel; } }

    public abstract class Wheel
    {
    }             

    private class PrivateWheel : Wheel
    {
        public int WheelSize { get; set; }
    }

    public static Wheel CreateWheel()
    {
        return new PrivateWheel();
    }
}