NEW: Start my new Ultimate Portfolio App course with a free Hacking with Swift+ trial! >>

How to conform to the Comparable protocol

Swift version: 5.2

Paul Hudson    @twostraws   

The Comparable protocol allows use to use the <, >, <=, and >= operators with conforming data types, which in turn means that Swift knows how to sort arrays of those types. Most of Swift’s built-in types support Comparable out of the box, but if you want your own type to conform to them then you need to implement < – from that Swift can provide default implementations of the other three operators.

The < function needs to accept two instances of your type, one of the left-hand side and one on the right, and return true if the left-hand object should be ordered before the right-hand object.

As an example, consider this simple Person struct:

struct Person {
    var name: String
}

That has one property called name, and we’re going to make Person conform to the Comparable protocol based on that property. This means writing a static method called < that takes two instances of Person and internally compares the name properties of each of them:

struct Person: Comparable {
    var name: String

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

With that in place you can now use < to compare two instances of Person like this:

let taylor = Person(name: "Taylor Swift")
let justin = Person(name: "Justin Bieber")
print(taylor < justin)
Hacking with Swift is sponsored by Fernando Olivares

SPONSORED Would you describe yourself as knowledgeable, but struggling when you have to come up with your own code? Fernando Olivares has a new book containing iOS rules you can immediately apply to your coding habits to see dramatic improvements, while also teaching applied programming fundamentals seen in refactored code from published apps.

Try the book!

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 8.0

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 3.7/5

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.