[Proposal:
https://github.com/apple/swift-evolution/blob/master/proposals/0108-remove-assoctype-inference.md
<https://github.com/apple/swift-evolution/blob/master/proposals/0108-remove-assoctype-inference.md>
]
I’m pretty concerned about completely removing this feature. Yes, it’s a
type-checker / decl-checker nightmare, but I think Paolo’s example in the
initial discussion showed how it’s being used effectively today. I’d much
rather have some kind of inference marker that maps one-to-one between an
associated type and a value requirement (method, initializer, property, or
subscript), also as brought up in the original discussion.
protocol OptionA {
associatedtype Index
@infers(Index)
var startIndex: Index { get }
var endIndex: Index { get }
}
protocol OptionB {
@inferredFrom(startIndex) // allows a full name here for overload resolution
associatedtype Index
var startIndex: Index { get }
var endIndex: Index { get }
}
protocol OptionC {
associatedtype Index in startIndex // sugar
var startIndex: Index { get }
var endIndex: Index { get }
}
OptionC is the prettiest, but OptionA is probably the most flexible (consider
overloading on associated types).
I know we want to lock down on things now, and I know we can do better in the
future, but I think inferring associated types is really quite common, and I’m
concerned about taking it out without giving people a good alternative. This is
just an impression, though.
Jordan_______________________________________________
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