[swift-users] make a static/class method return type be the subclass it is called with

[Pierre Monod-Broca]

Hello,

It looks that you have what you wanted because Event.Entity is an alias of Event. 

Pierre

> Le 5 janv. 2017 à 16:47, Dave Reed via swift-users <swift-users at swift.org> a écrit :
> 
> Is there a way to make a static or class method specify the return type be the actual class it is called with?
> 
> The example code below using protocols/extensions mostly works (the type is [Event.Entity] not [Event] but it seems to work.
> 
> If I try to make DDRCoreData a base class and Event subclass it, I'm only able to get the return type to be [DDRCoreData], not [Event] when I call it with Event.items(in: moc)
> 
> Here is the code that mostly works using protocols. Is there a better way to do this?
> 
> protocol DDRCoreData {
>    associatedtype Entity: NSManagedObject
> 
>    static func items(in context: NSManagedObjectContext, matching predicate: NSPredicate?, sortedBy sorters: [NSSortDescriptor]?) -> [Entity]
> }
> 
> extension DDRCoreData {
>    static func items(in context: NSManagedObjectContext, matching predicate: NSPredicate? = nil, sortedBy sorters: [NSSortDescriptor]? = nil) -> [Entity] {
>        var items: [Entity] = []
>        context.performAndWait {
>            let fetchRequest: NSFetchRequest<Entity> = Entity.fetchRequest() as! NSFetchRequest<Entity>
>            fetchRequest.predicate = predicate
>            fetchRequest.sortDescriptors = sorters
>            do {
>                items = try fetchRequest.execute() as [Entity]
>            } catch {
> 
>            }
>        }
>        return items
>    }
> }
> 
> @objc(Event)
> public class Event: NSManagedObject {
> 
> }
> 
> extension Event: DDRCoreData {
>    typealias Entity = Event
> }
> 
> // compiler says items is of type [Event.Entity]
> let items = Event.items(in: controller.managedObjectContext!)
> 
> Thanks,
> Dave Reed
> 
> 
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