CODEWITHSUNDEEP
swift
joels
joels

Reputation: 7711

Cannot special non-generic type AnyObject

public protocol Subscriber : class {
}
public struct Subscription {
    private weak var subscriber:AnyObject<Subscriber>? = nil
}

Why can't I use AnyObject with a protocol for this var?

Upvotes: 1

Views: 228

Answers (2)

Daniel Hall
Daniel Hall

Reputation: 13679

Swift doesn't allow combining a type and a protocol the way Objective-C does, although you can specify a combination of protocols. Since AnyObject is in fact a protocol, you can accomplish what you want to express above by writing:

public struct Subscription {
    private weak var subscriber:protocol<Subscriber, AnyObject>? = nil
}

This requires subscriber to conform to both the Subscriber and the AnyObject protocols.

In your case above, you actually don't need the AnyObject part since you made the Subscriber protocol a class protocol which essentially guarantees that any conforming type is also an AnyObject. So you could just write:

public struct Subscription {
    private weak var subscriber:Subscriber? = nil
}

But the protocol<Subscriber, AnyObject> approach would allow your Subscriber protocol to not be restricted to only class types, while making that specific subscriber weak var restricted to class types that implement Subscriber.

Upvotes: 4

JAL
JAL

Reputation: 42449

To refer to an object that conforms to a protocol, just use the protocol. Swift is not like Objective-C where you need to specify id<SomeProtocol>:

public struct Subscription {
    private weak var subscriber: Subscriber? = nil
}

You can also declare your protocol like this if you want to restrict usage to AnyObject, rather than using class:

public protocol Subscriber : AnyObject {
    // ...
}

Upvotes: 2

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