On 11.01.2018 1:54, Jordan Rose via swift-evolution wrote:
[Proposal:
https://github.com/apple/swift-evolution/blob/master/proposals/0194-derived-collection-of-enum-cases.md]
I think this is generally reasonable, and none of the names offend me enough to weigh in on that discussion. I do think
it's a little weird that @objc enums defined in Swift /cannot/ conform to ValueEnumerable, just because imported enums
won't. (But especially while knee-deep in SE-0192, I think it's /correct/ that imported enums won't. The exception could
be C enums marked `enum_extensibility(closed)`, but I'm not convinced we need that yet.)
The biggest problem I have is unavailable cases. An unavailable case /must not/ be instantiated—consider an enum where
some cases are only available on iOS and not macOS. (I bet we optimize based on this, which makes it all the more
important to get right.)
I think you should explicitly call out that the derived implementation only kicks in when ValueEnumerable is declared on
the enum itself, not an extension. Or if that's not the case, it should be limited to extensions in the same module as
the enum. (You could add "unless the enum is '@frozen'", but that's not really necessary.)
I'd also ask to append that information into the proposal, as IMO it is very
important point.
I was under impression that we'll be allowed to retroactively conform to ValueEnumerable for frozen enums from other
modules. Wouldn't this be a very requested feature of ValueEnumerable ? I.e. when we have a module with frozen enum, but
author of that enum didn't consider conforming to ValueEnumerable for some reason.
Vladimir.
I don't think this should be implemented with a run-time function; compile-time code generation makes more sense to me.
But that's an implementation detail; it doesn't change the language surface.
Jordan
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