[swift-evolution] [swift-dev] Re-pitch: Deriving collections of enum cases

[Jacob Bandes-Storch]

Re-reading this thread and thinking about it more, I think I agree :)
Updating again...

On Sat, Dec 30, 2017 at 3:44 PM, Chris Lattner <clattner at nondot.org> wrote:

> On Dec 30, 2017, at 3:12 PM, Jacob Bandes-Storch via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Sorry for the delay. I've just updated the proposal text to incorporate
> various changes, some contributed by others.
>
> https://github.com/jtbandes/swift-evolution/blob/case-
> enumerable/proposals/0000-derived-collection-of-enum-cases.md
>
>
> I would really love to see this happen.  I did a pass over the proposal, I
> strong suggest that you get Joe Groff’s input on this, because he has some
> opinions as well.
>
> IMO, the proposal looks really great except for one thing:   In "proposed
> solution”, I think it is very important that conformance to ValueEnumerable
> be explicitly requested in the code.  Specifically:
>
> enum Ma { case 马, 吗, 妈, 码, 骂, 麻, 🐎, 🐴 }
> Ma.allValues   // error.
>
> enum Ma : ValueEnumerable { case 马, 吗, 妈, 码, 骂, 麻, 🐎, 🐴 }
> Ma.allValues   // works!
>
>
> This is for two reasons:
> 1) Consistency with other similar features in Swift.  Types are not
> hashable just because their members could be.  This is because we want
> people to think about and explicitly opt into API features like this.
> 2) To align with our resilience design.  An enum with no value-associated
> cases today could acquire them in the future, and doing so would implicitly
> remove this conformance.  This would be surprising and bad.
>
> Thanks for pushing this forward!
>
> -Chris
>
>
>
>
>
>
> Robert's implementation
> <https://github.com/apple/swift-evolution/pull/114#issuecomment-337105126> is
> a good start, but will need to be updated to match the naming choice in the
> final proposal, and to use associatedtype.
>
> On Fri, Dec 8, 2017 at 9:19 PM, Step Christopher <
> schristopher at bignerdranch.com> wrote:
>
>> Has this stalled out again? I would like to help with the proposal and
>> even attempt implementation.
>>
>> I also need to catch up on the resilient discussion regarding enum case
>> ordering.
>>
>> On Nov 14, 2017, at 10:50 PM, Jacob Bandes-Storch via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>
>>
>> Jacob Bandes-Storch
>>
>> On Tue, Nov 14, 2017 at 9:06 PM, Brent Royal-Gordon <
>> brent at architechies.com> wrote:
>>
>>> On Nov 14, 2017, at 5:21 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>>
>>> 1. It must be possible to easily access the count of values, and to
>>>> access any particular value using contiguous `Int` indices. This could be
>>>> achieved either by directly accessing elements in the list of values
>>>> through an Int subscript, or by constructing an Array from the list of
>>>> values.
>>>>
>>>> 2. It must be possible to control the order of values in the list of
>>>> values, either by using source order or through some other simple,
>>>> straightforward mechanism.
>>>>
>>>
>>> OK, first of all, nowhere in the proposal text are these requirements
>>> stated as part of the use case. You're free to put forward new use cases,
>>> but here I am trying to design the most elegant way to fulfill a stated
>>> need and you're telling me that it's something other than what's written.
>>>
>>>
>>> Honestly, re-reading the proposal, it never cites a fully-formed use
>>> case. Instead, it cites several blog posts, Stack Overflow questions, and
>>> small code samples without digging in to the underlying reasons why
>>> developers are doing what they're doing. Most of the people discussing it
>>> so far seem to have had a tacit understanding that we wanted roughly
>>> Array-like access, but we haven't explicitly dug into which properties of
>>> an Array are important.
>>>
>>> (If anyone involved feels like they had a different understanding of the
>>> use case, please speak up.)
>>>
>>> I think this is a place where the proposal can be improved, and I'm
>>> willing to do some writing to improve it.
>>>
>>
>> For the record, I would be happy to add co-authors (or even relinquish
>> authorship entirely—I don't really care whose name is on this, it just
>> needs to happen!) if you or anyone else has improved wording, motivation,
>> justification, etc. to contribute.
>>
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>>
>>
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