Implementing equality would be made tedious again if we lose this.
```
enum Jams : Equatable {
case dmsr(Bool)
case kiss(Bool, Bool)
case pheromone(Int, Bool, Int)
public static func ==(lhs:Jams, rhs:Jams) -> Bool {
switch (lhs, rhs) {
case let (.dmsr(left), .dmsr(right)):
return left == right
case let (.kiss(left), .kiss(right)):
return left == right
case let (.pheromone(left), .pheromone(right)):
return left == right
case (.dmsr, _), (.kiss, _), (.pheromone, _):
return false
}
}
}
```
On Sun, Jan 22, 2017 at 4:51 AM, Robert Widmann via swift-evolution <
[email protected]> wrote:
> Sure. One of the first gadgets I wrote was a way of destructuring an
> array into a familiar cons-list kind of enum (https://github.com/typelift/
> Basis/blob/master/Basis/Array.swift#L9) which you use something like this
> with other non-trivial enums (https://github.com/typelift/Valence/blob/
> cf4353c64de93b98c460529b06b8175c9ecfb79b/Tests/SystemF.swift#L161).
>
> It's not strictly a problem for me to lose this feature, but it is gonna
> be a bit weird if we lose recursive match but also allow it for just plain
> old tuple patterns.
>
> ~Robert Widmann
>
> 2017/01/22 3:02、Daniel Duan <[email protected]> のメッセージ:
>
> FWIW, in all public Github repos with 5k+ stars whose language gets
> recognized as “Swift”, 576 enum cases has associated values and among them
> 55 has 2 values or more. After some very casual grepping I didn’t find a
> lot of usage of this particular pattern.
>
> Care to share some examples, Robert?
>
> - Daniel Duan
>
> On Jan 21, 2017, at 11:00 PM, Robert Widmann <[email protected]>
> wrote:
>
> I find myself doing this *a lot*, but maybe my problems are just more
> Algebra-shaped than most. That said, I appreciate this cleanup and lean +1
> (because you mentioned a way to partly keep this behavior).
>
> ~Robert Widmann
>
> 2017/01/19 18:14、Joe Groff via swift-evolution <[email protected]>
> のメッセージ:
>
>
> On Jan 19, 2017, at 2:58 PM, Daniel Duan <[email protected]> wrote:
>
>
>
> On Jan 19, 2017, at 2:29 PM, Joe Groff <[email protected]> wrote:
>
>
>
> On Jan 19, 2017, at 1:47 PM, Douglas Gregor via swift-evolution <
> [email protected]> wrote:
>
>
> This looks totally reasonable to me. A couple of comments:
>
>
> 1) Because this proposal is breaking the link between the associated value
> of an enum case and tuple types, I think it should spell out the rules that
> switch statements will use when matching an enum value against a a case
> with an associated value. Some kind of rules fell out of them being treated
> as tuple types, but they might not be what we want.
>
>
> I was about to bring up the same. Right now, an enum pattern works like
> .<identifier> <tuple-pattern>, where the <tuple-pattern> then recursively
> matches the payload tuple. In this model, it seems like we'd want to treat
> it more like .<identifier>(<pattern>, <pattern>, ...). Similar to how we
> lost "tuple splatting" to forward a bunch of arguments, we'd have to decide
> whether we lose the ability to match all parts of the payload into a tuple.
>
>
> I’m leaning towards “no” for simplicity of the language (and
> implementation). That means this would be source-breaking 😞. Will update
> the proposal and see how the rest of the feedback goes.
>
>
> It'd be a good idea to try to find examples of people doing this out in
> the wild too, to see how widespread it is as well as how onerous the
> workarounds for losing the feature would be.
>
> -Joe
>
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>
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>
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