I never had any problems with commas, as I always read them as conjunctive clauses, but I understand that an explicit conjunction may be less confusing. Personally, I’d prefer if there was no special syntax (aka Any<>) for existential types, whether generalised or not. I fail to see a principal difference between an existential type vardecl and a non-existential type vardecl: both can be described as sets of factual types, with non-existential declarations trivially being sets of cardinality one. Under this perspective, adopting different syntax for these cases feels like an idiosyncratic decision to me. I also disagree that Any<> makes existential types more readable, on contrary, they introduce visual clutter. A considerably complex existential definition could always be hidden behind a typealias.
Ideally, I’d like ALL type references in variable declarations be treated as existentials: the variable is declared as belonging to a certain set of factual types (in most cases this will trivially be a single factual type). IMO, this would result in a simple and concise system. It would also make type-erased wrappers unnecessary, simplifying the language. Best, Taras > On 02 Jun 2016, at 07:42, Austin Zheng via swift-evolution > <swift-evolution@swift.org> 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 > > <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. > > Best, > Austin > >> On Jun 1, 2016, at 10:17 PM, Chris Lattner <clatt...@apple.com >> <mailto:clatt...@apple.com>> wrote: >> >> >>> On Jun 1, 2016, at 9:53 PM, Austin Zheng <austinzh...@gmail.com >>> <mailto:austinzh...@gmail.com>> 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 > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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