Swift Check if Two Objects Conforming to a Protocol Are Referentially The Same

Question

I have a protocol that forms the base of many classes—in the example below, StaticFile and RemoteFile. I have a reference to a variable that points to the protocol

protocol ContainerDelegate {}

protocol FileProtocol {
    var delegate: ContainerDelegate? { get set }
}

class StaticFile: NSObject, FileProtocol {
    var delegate: ContainerDelegate?
}
class RemoteFile: NSObject, FileProtocol {
    var delegate: ContainerDelegate?
}

class Container: NSObject, ContainerDelegate {
    var item: FileProtocol

    override init() {}

    func something() {
        if item.delegate !== self { // This fails
        }
    }
}

I don’t even care about types really, I only want to see if the delegate is not the current object (by reference). What’s the best way to make the failing line work correctly?

Answer 1

You should try to upcast the delegate and then check for equality:

func something() {
    if item.delegate as? Container !== self {
        print("hi")
    }
}

Full working code example

protocol ContainerDelegate {}
protocol FileProtocol {
    var delegate: ContainerDelegate? { get set }
}

class StaticFile: NSObject, FileProtocol {
    var delegate: ContainerDelegate?
}

class Container: NSObject, ContainerDelegate {
    var item: FileProtocol

    func something() {
        if item.delegate as? Container !== self {
            print("hi")
        }
    }

    override init() {
        item = StaticFile()
    }
}

let c = Container()
let c2 = Container()

c.item.delegate = c2
c.something() // hi gets printed

c.item.delegate = c
c.something() // hi does **not** get printed