Casting generics

Question

Can someone help me with a work-around for this issue?

I have the following class:

public partial class FObjectSet<T> : IObjectSet<T> where T : class
{
...
}

I also have the following class:

public partial class FContext : IContext, IDisposable
{
    public ObjectSet<T> CreateObjectSet<T>() where T : class
    {
        var fakeObjectSet = new FObjectSet<T>();
        return (fakeObjectSet as IObjectSet<T>) as ObjectSet<T>;
    }
}

The CreateOjectSet method returns a null as the cast is not working.

ps The code above is trying to fake the System.Data.Objects.ObjectContext.CreateObjectSet method.

Answer 1

In your example, FObjectSet does not appear to inherit from ObjectSet. It only implements the IObjectSet interface.

If it did inherit from ObjectSet, you wouldn't need to cast it to a IObjectSet before casting it to an ObjectSet, in fact, you wouldn't need to cast it at all...

public partial class FObjectSet<T> : ObjectSet<T> where T : class
{
...
}

public partial class FContext : IContext, IDisposable
{
    public ObjectSet<T> CreateObjectSet<T>() where T : class
    {
        var fakeObjectSet = new FObjectSet<T>();
        return fakeObjectSet;
    }
}

Answer 2

This doesn't work because FObjectSet<T> doesn't extend ObjectSet<T> . You could return IObjectSet<T> instead, but I don't know if that would do what you want.