[swift-users] hashValue of enum cases (was Reducing Array<OptionSet> to OptionSet)

[Fritz Anderson]

On 3 Nov 2016, at 8:37 PM, Erica Sadun via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:

>     private enum StringEnum: String { case one, two, three }
>     public init(strings: [String]) {
>         var set = MyOptionSet()
>         strings.flatMap({ StringEnum(rawValue: $0) })
>             .flatMap({ MyOptionSet(rawValue: 1 << $0.hashValue) })
>             .forEach { set.insert($0) }
>         _rawValue = set.rawValue
>     }

I’m curious about relying on the hash value of an enum case being its declaration-order index. A sage (http://ericasadun.com/2015/07/12/swift-enumerations-or-how-to-annoy-tom/ <http://ericasadun.com/2015/07/12/swift-enumerations-or-how-to-annoy-tom/>) warns that this  is an implementation detail. I haven’t seen anything saying it is API. Has it been resolved?

It’s the most plausible implementation, but I’d think code that relies on case order would break silently (likely at widely-separated locations) if a case were inserted or removed. That suggests to me it’s not possible to regularize this behavior.

Folkloric API (like SEL ↔︎ char* in ObjC) makes me itch.

	— F

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