Swift Equatable on a protocol

Question

I don\'t think this can be done but I\'ll ask anyway. I have a protocol:

protocol X {}

And a class:

class Y:X {}

Answer 1

I came cross this same issue and I figured that the == operator can be implemented in the global scope (as it used to be), as opposed to a static func inside the protocol's scope:

// This should go in the global scope

public func == (lhs: MyProtocol?, rhs: MyProtocol?) -> Bool { return lhs?.id == rhs?.id }
public func != (lhs: MyProtocol?, rhs: MyProtocol?) -> Bool { return lhs?.id != rhs?.id }

Note that if you use linters such as SwiftLint's static_operator, you'll have to wrap that code around // swiftlint:disable static_operator to silent linter warnings.

Then this code will start compiling:

let obj1: MyProtocol = ConcreteType(id: "1")
let obj2: MyProtocol = ConcreteType(id: "2")
if obj1 == obj2 {
    print("They're equal.")
} else {
    print("They're not equal.")
}