[swift-evolution] [Review] SE-0194: Derived Collection of Enum Cases

David Waite david at alkaline-solutions.com
Mon Jan 8 22:57:54 CST 2018

> https://github.com/apple/swift-evolution/blob/master/proposals/0194-derived-collection-of-enum-cases.md <https://github.com/apple/swift-evolution/blob/master/proposals/0194-derived-collection-of-enum-cases.md>
> What is your evaluation of the proposal?
Generally +1

I would like the behavior of the generated ValueEnumerable to be defined, even if that behavior is based on the proposed implementation. Would this be declaration order? Would it be out of declaration order if a raw integer value was used and the cases did not have consistently increasing raw values?

I don’t know if there is an application compatibility suggestion here, such as ‘new enumerable values should be added to the end’.

I can also understand the value of not having the static property be an Array<T> to save memory, but instead be Array-like. To this end, I think the allValues property should have an additional constraint of an Index associatedtype of Int. I don’t know if there is an additional requirement for the indices being all the values from 0..<count for pedantry. 

I think the type annotated with ValueEnumerable also needs to at a minimum be Equatable to be generically useful.

I’d love to also suggest things like being Encodable, but if needed those can be proposed later.

allValues isn’t the perfect bike shed shade IMHO because of a dissonance in my own head, a carry-over from languages where enum values are singleton instances. For someone who can keep enum behavior straight in their head, I think the shade is perfectly fine.

> Is the problem being addressed significant enough to warrant a change to Swift?
I think so.

> Does this proposal fit well with the feel and direction of Swift?

> If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
I use Java’s version of this feature a fair bit. One common extension I see is to convert textual names to enum values, something that it doesn’t support well natively. 

> How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
A quick reading

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