Objects of interface, but constraint on type implementing the interface

I've a generic method with a constraint like below:

private string GetResult<T>(T myObject) where T : IDoSomething<T>
{
......
}

Now, the problem is that the IDoSomething is im开发者_高级运维plemented by the classes and not by classes interface and moreover the objects are always created using the interface as their type and not the class like:

IClassA myObject = new ClassA();

So, whenever the generic method is called, a cast must be made on myObject to forward it as a parameter.

Is there a way to avoid the cast and make the code work? (except the option of inheriting IDoSomething in IClassA)

No, I don't think you can avoid the cast, since the interface IClassA is not related in any way to IDoSomething.

Just the fact that some class that implements one interface also happens to implement another interface doesn't make the two interfaces compatible.

Even the assignment of a IClassA object back to a ClassA variable requires a explicit cast.

No, there's no way to avoid the cast in the way that you're doing it.

If you don't want IDoSomething<T> and IClassA to be related by extension and you don't want to use a variable typed with the concrete class, then there isn't any information for the compiler to use to infer that your object implements the right interface for the method without using a cast.

It depends. Are you just trying to get T? In that case, you could do:

private static string GetResult<T>(IDoSomething<T> myObject) {}

Then T will be inferred correctly from the interface (since IClassFoo will always inherit from it) and you won't have to cast.

If you want to pass it as T, though AND not have to cast it, then you're out of luck, there's not a relationship you can exploit.