[swift-evolution] [Pitch] Synthesized static enum property to iterate over cases

[Matthew Johnson]

Sent from my iPad

> On Sep 9, 2017, at 11:42 AM, gs. <griotspeak at gmail.com> wrote:
> 
> How does fragility play into this? Does this only work for fragile (closed) and internal/private/fileprivate enums?

That's a great question.  I think it would have to have that limitation.  Using Jordan's terminology, by definition a nonexhaustive cannot provide a complete list of all values.

> 
> TJ 
> 
>> On Sep 9, 2017, at 15:23, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> 
>> 
>> Sent from my iPad
>> 
>>> On Sep 9, 2017, at 7:33 AM, Brent Royal-Gordon <brent at architechies.com> wrote:
>>> 
>>>> On Sep 8, 2017, at 5:14 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> Here, people just want an array of all cases. Give them an array of all cases. When it's not possible (i.e., in the case of cases with associated values), don't do it.
>>> 
>>> 
>>> I agree it should be Int-indexed; that seems to be what people want from this.
>>> 
>>> I seem to recall that there is information about the available enum cases in the module metadata. If so, and if we're willing to lock that in as part of the ABI design, I think we should write—or at least allow for—a custom Int-indexed collection, because this may allow us to recurse into associated value types. If we aren't going to have suitable metadata, though, I agree we should just use an Array. There are pathological cases where instantiating a large Array might be burdensome, but sometimes you just have to ignore the pathological cases.
>>> 
>>> (The "infinite recursion" problem with associated values is actually relatively easy to solve, by the way: Don't allow, or at least don't generate, `ValuesEnumerable` conformance on enums with `indirect` cases.)
>> 
>> This is the direction I think makes the most sense in terms of how we should approach synthesis.  The open question in my mind is what the exact requirement of the protocol should be.  Should it exactly match what we synthesize (`[Self]` or an associated `Collection where Iterator.Element == Self, Index == Int`) or whether the protocol should have a more relaxed requirement of `Sequence where Iterator.Element == Self` like Tony proposed.
>> 
>>> 
>>> -- 
>>> Brent Royal-Gordon
>>> Architechies
>>> 
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