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

All people who say that you can't implement Equatable for a protocol just don't try hard enough. Here is the solution (Swift 4.1) for your protocol X example:

protocol X: Equatable {
    var something: Int { get }
}

// Define this operator in the global scope!
func ==(l: L, r: R) -> Bool {
    return l.something == r.something
}

And it works!

class Y: X {
    var something: Int = 14
}

struct Z: X {
    let something: Int = 9
}

let y = Y()
let z = Z()
print(y == z) // false

y.something = z.something
pirnt(y == z) // true

The only problem is that you can't write let a: X = Y() because of "Protocol can only be used as a generic constraint" error.