A Swift protocol requirement that can only be satisfied by using a final class

Question

I\'m modeling a owner/ownee scheme on Swift:

class Owner {
     // ...
}

protocol Ownee {
    var owner: Owner { get }
}
         


        

Answer 1

If you are coming to this thread just looking for a way to have subclasses inherit a method referring to its own type (type of Self) one workaround would be to parameterize the parent class on the child's type. e.g.

class Foo {
    func configure(_ block: @escaping (T)->Void) { }
}

class Bar: Foo { }

Bar().configure { $0... }

BUT... it also seems that you can add a method in a protocol extension that would not be considered to conform in the protocol itself. I don't fully understand why this works:

protocol Configurable {
    // Cannot include the method in the protocol definition
    //func configure(_ block: @escaping (Self)->Void)
}

public extension Configurable {
    func configure(_ block: @escaping (Self)->Void) { }
}

class Foo: Configurable { }

class Bar: Foo { }

Bar().configure { $0... }

If you uncomment the method in the protocol definition itself you'll get the Protocol 'Configurable' requirement 'configure' cannot be satisfied by a non-final class ('Foo') because it uses 'Self' in a non-parameter, non-result type position compile error.