C＃：泛型—推断泛型的泛型

Question

I don't even know how to ask this question so I'll just give the code example.

Here is the domain:

public interface ISubscriptionProvider<T>
{
    void Subscribe(Action<T> callback);
}

public class Notification {}

public class CurrentUserNotifications : ISubscriptionProvider<Notification>
{
    public void Subscribe(Action<Notification> callback) { }
}

Here is the method I want to make magical:

public void Subscribe<P, T>(Action<T> callback) where P : ISubscriptionProvider<T>
{
    // body left out -- code uses P
}

This works, and here is how you call it:

Subscribe<CurrentUserNotifications, Notification>((n) => Console.WriteLine(n));

So the question is: Is there any way to make it callable like this :

Subscribe<CurrentUserNotifications>((n) => Console.WriteLine(n));

Basically, can it infer that the action type should be just from the ISubscriptionProvider<T> .

This subscribe method lives on a static class (its a static method, I left that part out). The idea is that it will take care of constructing the ISubscriptionProvider<T> and keeping it a singleton (probably with structuremap). So in use:

Messages.Subscribe<CurrentUserNotifications>((n) => Console.WriteLine(n));

Thanks!

Update:

This is kinda off topic, but if any scala people read this ...

... is be an example of a higher kinded type? Something like:

public void Subscribe<P<T>>(Action<T> callback) { }

Where P<_> is the higher kinded type?

Answer 1

Why can't you just use

public void Subscribe<T>(Action<T> callback)
{
}

The type P Parameter is irrelevant in your scenario as it is never used.