Swift: Equatable with Optionals

Posted on July 6th, 2015

@andrewcbancroft recently wrote a great article about how Every Swift Value Type Should Be Equatable – go ahead and read it, I’ll wait…

One thing that stood out as missing from this article was comparing different sets of optional values. In the past, I have implemented the following equality for values to make sure optionals were covered:

// comparing two non-optionals
func ==(lhs: Place, rhs: Place) -> Bool { /* your implementation here */ }

// comparing one optional / one non-optional value
func ==(lhs: Place?, rhs: Place) -> Bool { /* your implementation here */  }

func ==(lhs: Place, rhs: Place?) -> Bool { /* your implementation here */ }

// comparing both optionals
func ==(lhs: Place?, rhs: Place?) -> Bool { /* your implementation here */ }

// comparing two non-optionals

func ==(lhs: Place, rhs: Place) -> Bool { /* your implementation here */ }

// comparing one optional / one non-optional value

func ==(lhs: Place?, rhs: Place) -> Bool { /* your implementation here */ }

func ==(lhs: Place, rhs: Place?) -> Bool { /* your implementation here */ }

// comparing both optionals

func ==(lhs: Place?, rhs: Place?) -> Bool { /* your implementation here */ }

I mentioned this in my Swift Newsletter this week, only to get the following responses on Twitter:

@NatashaTheRobot Re: Equatable, you should be able to skip the last one at least since Swift defines it.

— Rob Rix‎ (@rob_rix) July 6, 2015

@NatashaTheRobot @rob_rix and, unless something changed, you can skip the other two as well because of implicit conversion to optional

— anatomisation (@anatomisation) July 6, 2015

Of course, I had to see it for myself, so I tried this in the playground:

struct Place {
    let name: String
    let latitude: Double
    let longitude: Double
}

extension Place: Equatable {}

func ==(lhs: Place, rhs: Place) -> Bool {
    let areEqual = lhs.name == rhs.name &&
        lhs.latitude == rhs.latitude &&
        lhs.longitude == rhs.longitude
    
    return areEqual
}

let sf = Place(name: "San Francisco", latitude: 37.7833, longitude: 122.4167)
let sfOptional: Place? = Place(name: "San Francisco", latitude: 37.7833, longitude: 122.4167)
let sfOptional2: Place? = Place(name: "San Francisco", latitude: 37.7833, longitude: 122.4167)
let ny: Place? = Place(name: "New York", latitude: 40.7127, longitude: 74.0059)
let noPlace: Place? = nil
let noPlace2: Place? = nil

sf == sfOptional // true
sfOptional == sfOptional2 // true
sf == sfOptional2 // true
sfOptional2 == sf // true
sf == ny // false
ny == sfOptional2 // false
noPlace == noPlace2 // true
sfOptional == noPlace // false

struct Place {

let name: String

let latitude: Double

let longitude: Double

}

extension Place: Equatable {}

func ==(lhs: Place, rhs: Place) -> Bool {

let areEqual = lhs.name == rhs.name &&

lhs.latitude == rhs.latitude &&

lhs.longitude == rhs.longitude

return areEqual

}

let sf = Place(name: "San Francisco", latitude: 37.7833, longitude: 122.4167)

let sfOptional: Place? = Place(name: "San Francisco", latitude: 37.7833, longitude: 122.4167)

let sfOptional2: Place? = Place(name: "San Francisco", latitude: 37.7833, longitude: 122.4167)

let ny: Place? = Place(name: "New York", latitude: 40.7127, longitude: 74.0059)

let noPlace: Place? = nil

let noPlace2: Place? = nil

sf == sfOptional // true

sfOptional == sfOptional2 // true

sf == sfOptional2 // true

sfOptional2 == sf // true

sf == ny // false

ny == sfOptional2 // false

noPlace == noPlace2 // true

sfOptional == noPlace // false

Turns out, the Equatable implementation for optionals is not necessary. It just works!