[SOLVED] C#: Chained Linq methods and casting

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.GameObjects.Entity>" to "System.Collections.Generic.IEnumerable<T>"

Can anyone explain, why this happens?

Thank you!

Solution

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();
}