On Thu, Jun 2, 2016 at 12:42 AM, Austin Zheng via swift-evolution < [email protected]> wrote:
> Excellent. > > I put together a PR with a revised proposal containing the core team's > recommended approach. If anyone is curious they can see it here: > https://github.com/austinzheng/swift-evolution/blob/ef6adbe0fe09bff6c44c6aa9d73ee407629235ce/proposals/0095-any-as-existential.md > > Since this is the de-facto second round discussion thread, I'll start with > my personal opinion (which is *not* reflected in the PR): the '&' > separators in lieu of commas are a good idea, but I would still prefer the > types to be wrapped in "Any<>", at least when being used as existentials. > > My reasons: > > - Jordan Rose brought up a good point in one of the discussion threads > today: a resilience goal is to allow a library to add an associated type to > a protocol that had none and not have it break user code. If this is true > whatever syntax is used for existentials in Swift 3 should be a valid > subset of the generalized existential syntax used to describe protocol > compositions with no associated types. > > - I would rather have "Any<>" be used consistently across all existential > types eventually than have it only be used for (e.g.) existential types > with `where` constraints, or allowing two different representations of the > same existential type (one with Any, and one without). > > - I think any generalized existential syntax without delimiting markers > (like angle braces) is harder to read than syntax with such markers, so I > would prefer a design with those markers. > Agree with your reasons, but I'm still uncomfortable that things inside the angle brackets would behave differently here than elsewhere. Would it help to make a keyword out of `any` for existentials? Then you could have this: ``` func foo(value: any X & Y) ``` Best, > Austin > > On Jun 1, 2016, at 10:17 PM, Chris Lattner <[email protected]> wrote: > > > On Jun 1, 2016, at 9:53 PM, Austin Zheng <[email protected]> wrote: > > This was indeed a very thorough review by the core team. I'll prepare a v2 > proposal with this feedback taken into account so we can continue moving > things along. > > One quick question - is making whatever syntax is chosen for Swift 3 > "forward-compatible" with a future generalized existential feature a > concern? > > > Yes it is a concern, but we assume that the “X & Y” syntax will always be > accepted going forward, as sugar for the more general feature that is yet > to be designed. > > -Chris > > > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution > >
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