BLACK FRIDAY SALE: Save 50% on all my Swift books and bundles! >>

How to conform to the Hashable protocol

Swift version: 5.6

Paul Hudson    @twostraws   

In Swift, conforming to the Hashable protocol is often just as easy as adding Hashable to your conformance list. However, if you have custom requirements, or use properties that don’t all conform to Hashable, it takes a little more work.

Here’s an example struct we can work with:

struct iPad: Hashable {
    var serialNumber: String
    var capacity: Int

Because that conforms to the Hashable protocol and both its properties also conform to the Hashable protocol, Swift will generate a hash(into:) method automatically.

However, in this case we can see that serialNumber is enough to identify each iPad uniquely so hashing capacity isn’t needed. So, we can write our own implementation of hash(into:) that hashes just that one property:

func hash(into hasher: inout Hasher) {

You can add more properties to your hash by calling combine() repeatedly, and the order in which you add properties affects the finished hash value.

Swift uses a random seed every time it hashes an object, which means the hash value for any object is effectively guaranteed to be different between runs of your app.

This in turn means that elements you add to a set or a dictionary are highly likely to have a different order each time you run your app.

Hacking with Swift is sponsored by Guardsquare

SPONSORED AppSweep by Guardsquare helps developers automate the mobile app security testing process with fast, free scans. By using AppSweep’s actionable recommendations, developers can improve the security posture of their apps in accordance with security standards like OWASP.

Learn more

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 Pro Swift Buy Pro SwiftUI 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 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 Beyond Code

Was this page useful? Let us know!

Average rating: 4.3/5

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.