Type verification class with typical types

Question

I have a class like SomeController<A where A: ProtA>

I have some subclasses of type SubController: SomeController<SubA>

Here is a working example of how I am trying to enter validation:

 protocol SomeProtocol { } class SuperClass<A where A: SomeProtocol> { } class SubProtocol: SomeProtocol { } class SubClass: SuperClass<SubProtocol> { } func classTest<A where A: SomeProtocol>(classToTest: SuperClass<A>) { switch classToTest { case is SubClass: // Has warning 'Cast from SuperClass<A> to SubClass always fails' print("I'm a SubClass") default: print("Wasn't found") } } classTest(SubClass()) // Prints "I'm a SubClass" 

Functionally, the code does exactly what I want, however I am left with a ton of warnings saying Cast from SuperClass<A> to SubClass always fails

It’s clear that the types are related, and obviously the code works fine and doesn’t “always fail”, so this warning seems to be wrong. Is this the current constraint or edge case of the type system, or is there a way to make the warning go away?

Answer 1

The SuperClass definition, since it is a generic one, suppresses the warning. I also don't think you need a where clause to indicate that A matches SomeProtocol.

 func classTest<A:SomeProtocol, B:SuperClass<A>>(classToTest: B, useA:A) { switch classToTest { case is SubClass: // Has warning 'Cast from SuperClass<A> to SubClass always fails' print("I'm a SubClass") default: print("Wasn't found") } }