Set and protocols in Swift

Question

I would like to initialize a Set with values corresponding to the Hashable protocol and a custom protocol.

I tried :

protocol CustomProtocol: Hasha         


        

Answer 1

In Swift 3, one solution is to use the AnyHashable structure.

For instance, to create a Observers/Observable pattern, we could do :

protocol Observer {
    func observableDidSomething(_ observable: Observable)
}

class Observable {
    private var observersSet: Set = []

    private var observers: [Observer] {
        return observersSet.flatMap { $0 as? Observer }
    }

    func add(_ observer: O) where O : Observer, O : Hashable {
        observersSet.insert(observer)
    }

    func remove(_ observer: O) where O : Observer, O : Hashable {
        observersSet.remove(observer)
    }

    // ...

    private func doSomething() {
        // do something ...
        observers.forEach { $0.observableDidSomething(self) }
    }
} 

Notice that I separate the Hashable protocol from my protocol Observer.