CODEWITHSUNDEEP
swiftswift-protocols
user1264176
user1264176

Reputation: 1128

Swift. Protocols for delegate pattern in UIKit. NSObjectProtocol

Swift3. I am wondering how exactly UICollectionViewDelegate can be declared as a weak property.

If you check swift 'headers' you will see that it inherits from UIScrollViewDelegate which in turn inherits from NSObjectProtocol which is not marked as class-only protocol.

If I try to make my own protocol to use with delegate pattern as weak 'delegate' property I get compile time error 'weak' may only be applied to class and class-bound protocol types.

While I understand why compiler forces me to use class, I am wondering how UICollectionViewDelegate can get away with this. I would guess class is some kind of syntactic sugar but I would appreciate if you could explain me.

On a side note: Is there a pattern to deal with situations where I really need a protocol which could be adopted by both value and reference types but also "easily" managed from memory point of view (meaning weak references).

I am sorry for a bit fuzzy question.

Upvotes: 0

Views: 124

Answers (1)

i_am_jorf
i_am_jorf

Reputation: 54630

When you use the class keyword on a protocol definition, you're saying "this protocol only applies to classes, not Swift structs or enums."

When an object inherits from, or is, an Objective-C class or protocol, it by definition isn't a Swift struct or enum. So it doesn't need to specify.

Upvotes: 2

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