I actually like "any<P1, P2>". It does provide that very distinctive visual signal that any<> is not a generic type, and that 'any' is not itself a type, but rather a special keyword for constructing an existential:
Array<Int> // a generic type, Array, containing integers any<P1, P2> // a protocol composition of two protocols In this case, would we want to support "any<>" in addition to Any? The parsing issues should go away, since these are two different identifiers. Austin On Fri, May 20, 2016 at 12:04 PM, Matthew Johnson <[email protected]> wrote: > > On May 20, 2016, at 2:00 PM, Austin Zheng via swift-evolution < > [email protected]> wrote: > > I think you should submit this for review, but I also think you should > take the part of your older proposal to add class support to Any<...> and > submit it as a separate proposal. (I mean, the part where you can define > things like "Any<UIViewController, Protocol>" or "Any<class, Protocol>".) > > Yes, it is additive, but even getting that feature into Swift 3 would be > an enormous benefit if it can be implemented easily. And the core team is > probably better positioned than anyone else to determine whether that's > true. > > > Austin, what is your thought on switching to `any` rather than `Any` since > it does not behave like a user-defined generic type? The convention is for > types to be uppercase and keywords to be lowercase. This falls more into > the category of a keyword and has its own behavior distinct from the > behavior of all generic types. Making it stand out syntactically will help > to make that clear. > > > Austin > > On Fri, May 20, 2016 at 2:39 AM, Adrian Zubarev via swift-evolution < > [email protected]> wrote: > >> >> This is a follow up proposal to SE-0095 >> <https://github.com/apple/swift-evolution/blob/master/proposals/0095-any-as-existential.md> >> which >> should be considered for Swift 3 if SE-0095 will be accepted. >> >> Here is the formatted draft: >> https://github.com/DevAndArtist/swift-evolution/blob/master/proposals/nnnn-ban-redundancy-in-any-existential.md >> >> Please provide your feedback in this thread, and don’t make a race who is >> making a better proposal on the exact same topic. >> >> If you spot any types or other mistakes I’d be happy to see you pointing >> me to them. ;) >> >> -- >> Adrian Zubarev >> Sent with Airmail >> >> Disallow redundant Any<...> constructs >> >> - Proposal: SE-NNNN >> >> <https://github.com/apple/swift-evolution/blob/master/proposals/NNNN-name.md> >> - Author: Adrian Zubarev <https://github.com/DevAndArtist> >> - Status: Awaiting review >> - Review manager: TBD >> >> Introduction >> >> This is a follow up proposal to SE–0095 >> <https://github.com/apple/swift-evolution/blob/master/proposals/0095-any-as-existential.md>, >> if it will be accepted for Swift 3. The current concept of Any<...> >> introduced in SE–0095 will allow creation of redundant types like Any<A> >> == A. I propose to disallow such redundancy in Swift 3 to prevent >> breaking changes in a future version of Swift. >> >> Swift-evolution thread: [Proposal] Disallow redundant Any<...> constructs >> Motivation >> >> If SE–0095 will be accepted there will be future proposals to enhance its >> capabilities. Two of these will be *Any-type requirement* (where *type* >> could be class, struct or enum) and *Class requirement*. Without any >> restrictions these will introduce more redundancy. >> >> As said before it is possible to create redundant types like Any<A> == A >> or endless shadowed redundant nesting: >> >> typealias A_1 = Any<A> >> typealias A_2 = Any<A_1> >> typealias A_3 = Any<A_2> >> /* and so on */ >> >> This proposal should ban redundancy right from the beginning. If there >> might be any desire to relax a few things, it won’t introduce any breaking >> changes for Any<...> existential. >> Proposed solution >> >> 1. >> >> If empty Any<> won’t be disallowed in SE–0095, we should disallow >> nesting empty Any<> inside of Any<...>. >> 2. >> >> Disallow nesting Any (type refers to current typealias Any = >> protocol<>) inside of Any<...>. >> 3. >> >> Disallow Any<...> containing a single Type like Any<Type>. >> >> The first three rules will ban constructs like Any<Any<>, Type> or >> Any<Any, >> Type> and force the developer to use Type instead. >> 4. Disallow nesting a single Any<...> inside another Any<...>. >> - e.g. Any<Any<FirstType, SecondType>> >> 5. >> >> Disallow same type usage like Any<A, A> or Any<A, B, A> and force the >> developer to use A or Any<A, B> if A and B are distinct. >> 6. >> >> Disallow forming redundant types when the provided constraints are >> not independent. >> >> // Right now `type` can only be `protocol` but in the future Any<...> >> // could also allow `class`, `struct` and `enum`. >> // In this example `B` and `C` are distinct. >> type A: B, C {} >> >> // all following types are equivalent to `A` >> Any<A, Any<B, C>> >> Any<Any<A, B>, C> >> Any<Any<A, C>, B> >> Any<A, B, C> >> Any<A, B> >> Any<A, C> >> >> - >> >> If all contraints form a known Type provide a Fix-it error >> depending on the current context. If there is more than one Type, >> provide all alternatives to the developer. >> - >> >> Using Any<...> in a generic context might not produce a Fix-it >> error: >> >> protocol A {} >> protocol B {} >> protocol C: A, B {} >> >> // there is no need for `Fix-it` in such a context >> func foo<T: Any<A, B>>(value: T) {} >> >> >> Impact on existing code >> >> These changes will break existing code. Projects abusing Any<...> to >> create redundant types should be reconsidered of usings the equivalent >> Type the compiler would infer. One would be forced to use A instead of >> Any<A> for example. A Fix-it error message can help the developer to >> migrate his project. >> Alternatives considered >> >> - Leave redundancy as-is for Swift 3 and live with it. >> - Deprecate redundancy in a future version of Swift, which will >> introduce breaking changes. >> >> >> _______________________________________________ >> swift-evolution mailing list >> [email protected] >> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution > > >
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