How do you remove an element from an array of protocols in Swift?

Question

Swift's protocol implementation is really driving me crazy right now. I have an array observers defined over a custom protocol Observing and I am trying to remove an element from that array given the element, but Swift is complaining that Observing doesn't implement Identifiable (which I think is actually another of my own protocols, unless there's also a system protocol called that). All I want to do is a reference comparison and remove the actual object. I don't care about performing any kind of comparison on the objects.

var observers = [Observing]()

func removeObserver( observer: Observing ) {
    for i in 0 ..< self.observers.count {
        if self.observers[i] == observer { // <='Observing' is not convertible to 'Identifiable'...?
            self.observers.removeAtIndex(i)
            break
        }
    }
}

Answer 1

The == operator checks for value-equality in Swift, and for there is no default implementation for it. What you want is reference equality, which you can get using === and !== in Swift.

See the documentation for more details.

Identity Operators

Because classes are reference types, it is possible for multiple constants and variables to refer to the same single instance of a class behind the scenes. (The same is not true for structures and enumerations, because they are always copied when they are assigned to a constant or variable, or passed to a function.)

It can sometimes be useful to find out if two constants or variables refer to exactly the same instance of a class. To enable this, Swift provides two identity operators:

Identical to (===) Not identical to (!==)

Note that for the === operator to work, the objects must conform to the AnyObject protocol. You can guarantee this by suffixing the protocol with ": class", like this:

protocol SomeProtocol : class { ... }