C#: Chained Linq methods and casting

I have a little game, where I implemented some collision detection. Now I want to get a list of all items of a specific type, which are colliding with the current "Entity" object. I want to do something like this:

    public List<T> GetCollidingObjects<T>() where T : Entity
    {
        return this.Game.World.Entities
            .AsParallel()
            .Where(e => e.IsColliding(this))
            .Where(e => e is T)
            .ToList<T>();
    }

I get the following error:

Instance argument: cannot convert from "System.Linq.ParallelQuery<GameName.开发者_JAVA百科GameObjects.Entity>" to "System.Collections.Generic.IEnumerable<T>"

Can anyone explain, why this happens?

Thank you!

---

You cannot use ToList() like that. The generic parameter you supply (if you choose to do so) must match the type of the sequence. It's a sequence of Entity, not T.

Anyway, you should use OfType() to do the filtering, that's what it's there for.

public List<T> GetCollidingObjects<T>() where T : Entity
{
    return this.Game.World.Entities
        .OfType<T>()
        .AsParallel()
        .Where(e => e.IsColliding(this))
        .ToList();
}

---

Jeff Mercado's answer is correct, but can be stated more plainly.

.Where(e => e is T)

This call to Enumerable.Where<Entity> returns an IEnumerable<Entity> (a filtered version of the source, which is an IEnumerable<Entity>). The call does not return an IEnumerable<T>.

Enumerable.Select<TSource, TResult> and Enumerable.OfType<TResult> can return an IEnumerable with a type different than the source:

.Where(e => e is T)
.Select(e => e as T)

or

.Select(e => e as T)
.Where(e => e != null)

or

 .OfType<T>()