“Public” nested classes or not

Question

Suppose I have a class \'Application\'. In order to be initialised it takes certain settings in the constructor. Let\'s also assume that the number of settings is so many th

Answer 1

I think it's fine. This is basically the builder pattern, and using nested classes works pretty well. It also lets the builder access private members of the outer class, which can be very useful. For instance, you can have a Build method on the builder which calls a private constructor on the outer class which takes an instance of the builder:

public class Outer
{
    private Outer(Builder builder)
    {
        // Copy stuff
    }

    public class Builder
    {
        public Outer Build()
        {
            return new Outer(this);
        }
    }
}

That ensures that the only way of building an instance of the outer class is via the builder.

I use a pattern very much like this in my C# port of Protocol Buffers.