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

[C. Keith Ray]

good point - type safety would prevent it from compiling.

also, the controllers are subclasses of  NSFetchedResultsController<NSManagedObject>

but the delegate method takes a different type:  NSFetchedResultsController<NSFetchRequestResult>

NSManagedObject != NSFetchRequestResult



--
C. Keith Ray
Senior Software Engineer / Trainer / Agile Coach
* http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf



> On Oct 7, 2017, at 10:32 PM, Glen Huang <heyhgl at gmail.com> wrote:
> 
> I need to do things differently in the shared delegate based on the controller type, so this probably won’t work. But thanks, I believe it will come in handy when I do need to branch on controllers themselves.
> 
> I do have a question though, since the method is a callback, and its signature is changed (with "Thing &” added), will NSFetchedResultsController be able to find it and call it? 
> 
>> On 8 Oct 2017, at 12:14 AM, C. Keith Ray <keithray at mac.com <mailto:keithray at mac.com>> wrote:
>> 
>> Or make a base class for both Controller classes which defines todo () and override todo() in each Controller class.
>> 
>> --
>> C. Keith Ray
>> 
>> * https://leanpub.com/wepntk <https://leanpub.com/wepntk> <- buy my book?
>> * http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf <http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf>
>> * http://agilesolutionspace.blogspot.com/ <http://agilesolutionspace.blogspot.com/>
>> 
>> On Oct 7, 2017, at 9:12 AM, C. Keith Ray <keithray at mac.com <mailto:keithray at mac.com>> wrote:
>> 
>>> You should be able to do this to avoid casting.(I think)
>>> 
>>> protocol Thing {
>>>    func todo()
>>> }
>>> 
>>> class Controller1: NSFetchedResultsController<NSManagedObject>, Thing {
>>>     func todo () {doOneThing}
>>> }
>>> class Controller2: NSFetchedResultsController<NSManagedObject>, Thing {
>>>     func todo () {doAnotherThing}
>>> }
>>> 
>>> func controllerWillChangeContent(_ controller: Thing & NSFetchedResultsController<NSFetchRequestResult>) {
>>>     controller.todo()
>>>     ...
>>> }
>>> 
>>> --
>>> C. Keith Ray
>>> 
>>> * https://leanpub.com/wepntk <https://leanpub.com/wepntk> <- buy my book?
>>> * http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf <http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf>
>>> * http://agilesolutionspace.blogspot.com/ <http://agilesolutionspace.blogspot.com/>
>>> 
>>> On Oct 6, 2017, at 11:28 PM, Glen Huang via swift-users <swift-users at swift.org <mailto: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 <mailto:swift-users at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-users <https://lists.swift.org/mailman/listinfo/swift-users>
> 

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