Question

I am just starting to get to grips with generics and am (ab)using them to refactor a fairly complex section of my code (I’ve only been using c# for a little while but am fairly experienced in other languages).

I have an inheritance structure where my classes extend a base class. In the base class I have most of the functionality implemented. But I want to be able to associate these children classes with instances of their siblings.

Here is a simplification of some of the relevant code:

class ParentClass<T>
    where T : ParentClass<T>, new()
{

    public static T Create()
    {
        return new T();
    }

    private object joinedItem;

    public void Join<TJoinee>(TJoinee item)
        where TJoinee : ParentClass<TJoinee>, new()
    {
        joinedItem = item;
    }

}

class ChildOne : ParentClass<ChildOne>
{
}

class ChildTwo : ParentClass<ChildTwo>
{
}

With this code in place I can do something like:

var a = ChildOne.Create();
a.Join(new ChildTwo());

The problem is that I needed to type joinedItem as object when really I want to type it as ParentClass<Something>. Is it possible to prescribe a more specific type to joinedItem? Or am I just horribly abusing the language and should be taking a completely different approach?

Answer 1

Could you extract an interface from ParentClass<T> that is not dependent on T? That way joinedItem could be typed to the interface.

That seems to be as far as you can take what it looks like you’re trying to do (join ParentClass<T> instances to ParentClass<U> instances).

If there is nothing in that ParentClass<T> interface that is not dependant on T, then it will be difficult to find a more useful interface than object without knowing T.