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

[Dave Reed via swift-users]

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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