Question

I would like to specify a constraint which is another type with a generic argument.

class KeyFrame<T> {     public float Time;     public T Value; }  // I want any kind of Keyframe to be accepted class Timeline<T> where T : Keyframe<*> { } 

But this cannot be done in c# as of yet, (and I really doubt it will ever be). Is there any elegant solution to this rather than having to specify the type of the keyframe argument?:

class Timeline<TKeyframe, TKeyframeValue>       where TKeyframe : Keyframe<TKeyframeValue>, { } 

Answer 1

Read about this from Eric Lippert’s blog Basically, you have to find a way to refer to the type you want without specifying the secondary type parameter.

In his post, he shows this example as a possible solution:

public abstract class FooBase {   private FooBase() {} // Not inheritable by anyone else   public class Foo<U> : FooBase {...generic stuff ...}    ... nongeneric stuff ... }  public class Bar<T> where T: FooBase { ... } ... new Bar<FooBase.Foo<string>>() 

Hope that helps, Troy