In apple's implementation of Identifiable
the required function is
associatedtype ID
var id: Self.ID { get }
why is self required? What is the difference between that and
associatedtype ID
var id: ID { get }
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erotsppa
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`Self` represents the type that conforms to the protocol. – Leo Dabus Oct 10 '20 at 00:33
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yes I understand that, but why is it there? The second code already does that – erotsppa Oct 10 '20 at 00:34
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It is not required. You can omit it most of the time. – Leo Dabus Oct 10 '20 at 00:37
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They probably have added to be able to refer to it in their documentation. https://stackoverflow.com/questions/64286377/swift-parsing-data-error-swift-decodingerror-datacorrupted?noredirect=1#64287150 – Leo Dabus Oct 10 '20 at 00:44
1 Answers
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I think this is just a convention Apple uses when writing their documentation. They write all their associated types with the Self. prefix. Examples: 1, 2, 3. This is so that it is clear what is an associated type, and what isn't. If the declaration for Identifiable.id has instead been written like:
var id: ID { get }
To someone who's never used SwiftUI before, it is unclear whether ID is an entirely separate, top-level type, or an associated type. If it said Self.ID, however, it is clear that ID is an associated type of a protocol.
Other than that, the Self. prefix does not mean anything special. It's just like the self. prefix when referring to a instance member. It is optional in most cases. Just like the self. prefix, you probably need Self. to resolve name conflicts in some situations, though I can't think of any right now.
Apple also seems to have a convention for nested types - to always write out OuterTypeName.InnerTypeName, when just InnerTypeName is enough. Example:
var keyDecodingStrategy: JSONDecoder.KeyDecodingStrategy
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