[swift-users] How to check the type of a concrete class that inherits from a generic class?

[Glen Huang]

Done, https://bugs.swift.org/browse/SR-6083 <https://bugs.swift.org/browse/SR-6083>

In the mean time, is there any workaround? Or it’s not possible to check the concrete type without this issue being fixed?

> On 7 Oct 2017, at 2:44 PM, Slava Pestov <spestov at apple.com> wrote:
> 
> Oh I see. I think the problem is that with Objective-C generics, you can always cast from Foo<A> to Foo<B>, because the type parameters do not really exist. Swift’s type checking logic for casts assumes Swift generic semantics, where in general Foo<A> and Foo<B> are unrelated types.
> 
> Do you mind filing a bug?
> 
> Slava
> 
>> On Oct 6, 2017, at 11:40 PM, Glen Huang <heyhgl at gmail.com> wrote:
>> 
>> NSFetchedResultsController is the class from Core Data: 
>> 
>> https://developer.apple.com/documentation/coredata/nsfetchedresultscontroller
>> 
>>> On 7 Oct 2017, at 2:38 PM, Slava Pestov <spestov at apple.com> wrote:
>>> 
>>> Can you post a self-contained example, including the declaration of NSFetchedResultsController?
>>> 
>>> Slava
>>> 
>>>> On Oct 6, 2017, at 11:28 PM, Glen Huang via swift-users <swift-users at swift.org> wrote:
>>>> 
>>>> Hi,
>>>> 
>>>> I defined some concrete classes inheriting from a generic class like this:
>>>> 
>>>> class Controller1: NSFetchedResultsController<NSManagedObject> {}
>>>> class Controller2: NSFetchedResultsController<NSManagedObject> {}
>>>> 
>>>> And I assign them a shared delegate, and in the delegate method:
>>>> 
>>>> func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
>>>> 
>>>> I want to test the concrete type of controller, doing things differently for Controller1 and Controller2.
>>>> 
>>>> But doing the following gives me a warning: Cast from 'NSFetchedResultsController<NSFetchRequestResult>' to unrelated type 'Controller1’ always fails
>>>> 
>>>> switch controller {
>>>> case is Controller1:
>>>>     // ...
>>>> default:
>>>>     break
>>>> }
>>>> 
>>>> I wonder what’s the correct way to check the concrete type?
>>>> 
>>>> Regards,
>>>> Glen
>>>> _______________________________________________
>>>> swift-users mailing list
>>>> swift-users at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-users
>>> 
>> 
> 

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