Swift version: 5.6
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.
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Available from iOS 8.0 – learn more in my book Swift Design Patterns
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
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