Generic XOR Swap in Swift

Question

Today I was reading about XOR Swaps, and figured I would try to implement a function in Swift that would do this. I successfully wrote a non-generic version of this function:

import UIKit

func xorSwap (inout x: Int, inout y: Int) {
    if x != y {
        x ^= y
        y ^= x
        x ^= y
    }
}


var a = 10
var b = 20

xorSwap(&a, &b)

println(a) //=> 20
println(b) //=> 10

I then tried writing a generic version of this, but the compiler complained that 'T is not identical to Bool'. I'm assuming there's another protocol I need to declare conformance to, but I'm not sure what that is. Here's the attempt at a generic version:

import UIKit

func xorSwap<T: Equatable> (inout x: T, inout y: T) {
    if x != y {
        x ^= y
        y ^= x
        x ^= y
    }
}


var a = 10
var b = 20

xorSwap(&a, &b)

println(a)
println(b)  

Does anyone have a better understanding of this and can help me fill the gaps in my understanding? Thanks.

Answer 1

You can use built-in BitwiseOperationsType

func xorSwap<T: protocol<BitwiseOperationsType, Equatable>> (inout x: T, inout y: T) {
    if x != y {
        x ^= y
        y ^= x
        x ^= y
    }
}

var a = 10
var b = 20

xorSwap(&a, &b)

println(a) // -> 20
println(b) // -> 10

---

var a = NSStringCompareOptions.CaseInsensitiveSearch
var b = NSStringCompareOptions.BackwardsSearch

xorSwap(&a, &b)

a == .BackwardsSearch // -> true
b == .CaseInsensitiveSearch // -> true