NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

What’s the difference between a protocol and a class?

Swift version: 5.2

Paul Hudson    @twostraws   

When writing protocol-oriented Swift, protocols and classes become fairly similar, but they are never the same.

In their basic form, a protocol describes what an unknown type of object can do. You might say it has two or three properties of various types, plus methods. But that protocol never includes anything inside the methods, or provides actual storage for the properties.

In a more advanced form, you can write extensions on your protocols that provide default implementations of the methods. You still can’t provide storage for properties, however.

In comparison, classes are concrete things. While they might adopt protocols – i.e., say they implement the required properties and methods – they aren’t required to do that. You can create objects from classes, whereas protocols are just type definitions. Try to think of protocols as being abstract definitions, whereas classes and structs are real things you can create.

Hacking with Swift is sponsored by Paw

SPONSORED Use Paw to build, test and describe web APIs. Paw has a lightning fast native macOS interface to compose requests, collaborate in real-time on API specs, and generate client code for your applications. You can import and export API definitions.

Discover Paw for Mac

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: 4.0/5

Link copied to your pasteboard.