How to restrict a protocol to classes
Swift version: 5.4
There are some occasions when your protocol relies on reference semantics to work, which in practice means it can be adopted only by classes. For example, you might want to use the identity operator (===) to compare two instances of a conforming type, or you might want to change properties inside the type without relying on mutating methods.
To restrict your protocol in this way, make it inherit from AnyObject like this:
protocol Authenticatable: AnyObject {
func authenticate() -> Bool
}Note: Some older Swift code uses class for this restriction, but AnyObject is correct for modern Swift.
SPONSORED Join a FREE crash course for iOS devs who want to become complete senior developers — from October 18th to 24th. Learn how to apply iOS app architecture patterns through a series of lectures and practical coding sessions.
Sponsor Hacking with Swift and reach the world's largest Swift community!
Available from iOS 8.0 – learn more in my book Swift Design Patterns
Similar solutions…
- What are size classes?
- How to create different layouts using size classes
- What is protocol-oriented programming?
- What is a protocol associated type?
- What is a protocol?
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
