Class declared inside of another class in C#

Question

I am working on some legacy code and have come across something that I\'m not sure of. We have a class y that is declared inside of another class x.

Answer 1

This has permissions implications. A top-level "class y" would be "internal" - however, here "y" is private to "x". This approach is helpful for implementation details (for example cache rows etc). Likewise, y has access to all private state of x.

There are also implications with generics; x.y is generic "of T", inherited from the outer class. You can see this here, where Bar has full use of T - and note that any static fields of Bar are scoped per-T.

class Foo {
    void Test(T value) {
        Bar bar = new Bar();
        bar.Value = value;
    }
    class Bar {
        public T Value { get; set; }
    }
}

Often people incorrectly think they need to define Bar as Bar - this is now (effectively) doubly generic - i.e. Foo - where TOld is the (now unavailable) T from Foo. So don't do that! Or if you want it to be doubly-generic, pick different names. Fortunately, the compiler warns you about this...