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How to conform to the Equatable protocol

Paul Hudson       @twostraws

The Equatable protocol is what allows two objects to be compared using ==, and it’s surprisingly easy to implement. In fact, if you’re using Swift 4.1 or later and meet certain criteria, it’s trivial to implement!

First, here’s a struct we can work with:

struct Person {
    var name: String
    var age: String
}

To make that Equatable you need to add the Equatable conformance like this:

struct Person: Equatable {
    var name: String
    var age: String
}

If you’re using Swift 4.1 or later, and have no special requirements, that’s your code complete – Swift can take care of the rest.

If you’re on an earlier version of Swift, if you don’t just want to check all properties for equality, or if any of your properties are not also Equatable, then you need to write your own == function like this:

static func ==(lhs: Person, rhs: Person) -> Bool {
    return lhs.name == rhs.name && lhs.age == rhs.age
}

Put that inside the Person struct. Because that’s your own function you can make it do any comparisons you like. Swift’s default Equatable implementation will check all properties for equality, so if you have one property that is guaranteed to be unique adding your own Equatable implementation is a good idea.

Available from iOS 8.0 – learn more in my book Pro Swift

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