CODEWITHSUNDEEP
c#genericsinterfacecasting
DevDave
DevDave

Reputation: 6888

Cast T as having an interface?

Supposing I have a method:

public void DoStuff<T>() where T : IMyInterface {
 ...
}

And elsewhere in a different method I want to call

public void OtherMethod<T>() where T : class {
...
if (typeof(T) is IMyInterface) // have ascertained that T is IMyInterface
   DoStuff<T>();
}

Is there some way I can cast T as having my interface?

DoStuff<(IMyInterface)T> and other similar variations wouldn't work for me.

Edit: thanks for pointing out that typeof(T) is IMyInterface is the wrong way to check for the interface and should instead be called on an actual instance of T.

Edit2: I found that (IMyInterface).IsAssignableFrom(typeof(T)) worked in checking for the interface.

Upvotes: 2

Views: 1686

Answers (3)

D Stanley
D Stanley

Reputation: 152521

This line is wrong:

if (typeof(T) is IMyInterface) // have ascertained that T is IMyInterface
   DoStuff<T>();

typeof(T) returns a Type, which will never be a IMyinterface. If you have an instance of T, you can use

if (instanceOfT is IMyInterface) // have ascertained that T is IMyInterface
   DoStuff<T>();

or

if (instanceOfT is IMyInterface) // have ascertained that T is IMyInterface
   DoStuff<IMyInterface>();

Otherwise you could use reflection as Tim S suggests.

Upvotes: 1

laurie
laurie

Reputation: 708

You can use the same syntax to inherit from multiple interfaces:

public void OtherMethod<T>() where T : class, IMyInterface {
...
}

Upvotes: 2

Tim S.
Tim S.

Reputation: 56536

I think the most straightforward way to do that is with reflection. E.g.

public void OtherMethod<T>() where T : class {
    if (typeof(IMyInterface).IsAssignableFrom(typeof(T))) {
        MethodInfo method = this.GetType().GetMethod("DoStuff");
        MethodInfo generic = method.MakeGenericMethod(typeof(T));
        generic.Invoke(this, null);
    }
}

Upvotes: 3

Related Questions