I think the parentheses are the fundamental aspect of the suggestion :). Let me turn the question around. If tuples were declared like this:
let myTuple : Int, String, Bool = (10, "hello", false) would the type be more or less readable? I find it a lot more difficult to immediately parse than: let myTuple : (Int, String, Bool) = (10, "hello", false) At the same time, nobody's complained about tuple type parentheses getting in the way. We're trying to establish a syntax that will hopefully be used for things significantly more complicated than tuple definitions, which are just a list of types. I think readability is a major concern. Typealiases should be supported, but they shouldn't be required to make the feature useable. Finally, wouldn't we need some delimiter for nested existential definitions anyways? Now you have the confusing situation where the outside definition has no delimiters, but the inside ones do: // Why does the inner existential look fundamentally different than the outer one? // Not to mention, visually parsing the boundaries of this type when you look at it in a function signature let x : Protocol1, Protocol2, (Protocol 3 where .Foo == Int) where Protocol2.Bar : Baz I hope that explains my reasoning. Best, Austin > On May 27, 2016, at 9:28 AM, Matthew Johnson <[email protected]> wrote: > > > > Sent from my iPad > > On May 27, 2016, at 11:18 AM, Austin Zheng <[email protected] > <mailto:[email protected]>> wrote: > >> Here's a strawman idea. >> >> What if we go with '&' and 'where', but we enclose the whole thing in >> parentheses? >> >> (class & Protocol1 & Protocol2 where .Foo == Int, .Bar : Baz) >> >> There are a couple of reasons I propose this syntax: >> >> - It makes it very clear where the definition of the type begins and ends. I >> understand people really despise angle brackets, but I really want some way >> to visually delineate the boundaries of the type. Plus, I imagine it makes >> syntax a little easier to parse and preemptively forbids some ambiguities. >> >> - It's a structural, not nominal, type, like a tuple, so it uses parens as >> well. This reserves "<" and ">" for generic types. >> >> - The '&' is easily understood - "Protocol1" *and* "Protocol2". It's also a >> signal that order doesn't matter - just like how order matters with things >> that use commas, like argument lists, tuples, and array members, order >> doesn't generally matter with bitwise or logical 'and' operators. >> >> - If we ever decide to have union types, we have a very elegant third form >> of nominal type syntax that naturally falls out: (MyClass1 | MyClass2 | >> MyClass3). >> >> Thoughts? > > Generally in favor. But I would not require the parentheses. I believe they > would be allowed optionally automatically, just as (Int) is the same as Int > (because single element tuples don't exist and the underlying type is used > directly instead). It seems better to leave parentheses up to a matter of > style. > > >> >> Austin >> >> >>> On May 27, 2016, at 9:07 AM, Thorsten Seitz via swift-evolution >>> <[email protected] <mailto:[email protected]>> wrote: >>> >>> >>>> Am 27.05.2016 um 16:54 schrieb Matthew Johnson <[email protected] >>>> <mailto:[email protected]>>: >>>> >>>>> >>>>> On May 27, 2016, at 8:18 AM, Thorsten Seitz via swift-evolution >>>>> <[email protected] <mailto:[email protected]>> wrote: >>>>> >>>>> Personally I think `&` is more lightweight (and it is established in >>>>> other languages like Ceylon and Typescript) and `where` is more >>>>> expressive (and established in Swift for introducing constraints), so I >>>>> would stay with these. >>>> >>>> I agree. If we can make `&` with `where` work syntactically it would be >>>> nice to go in this lighter weight direction. If we decide to do that the >>>> question then becomes what to do with `protocol`. Would it be feasible to >>>> replace it with `&` in Swift 3 if we decide on that direction? >>> >>> Yep. `protocol` should be replaced with `&` in that case. >>> >>> -Thorsten >>> >>> >>>> >>>>> >>>>> -Thorsten >>>>> >>>>> >>>>>> Am 27.05.2016 um 14:34 schrieb Vladimir.S <[email protected] >>>>>> <mailto:[email protected]>>: >>>>>> >>>>>> Btw, in case we have `where` keyword in syntax related to >>>>>> types/protocols (when defining constrains. and not some symbol like >>>>>> '>>'.. don't know, for example), why we can't have 'and' keyword also >>>>>> when discuss the syntax of type/protocol conjunction? >>>>>> I.e. >>>>>> >>>>>> let x: P and Q >>>>>> let x: P and Q where P.T == Q.T >>>>>> let x: P and Q and R >>>>>> >>>>>> or, for consistency, as I understand it, we should have >>>>>> let x: P & Q >> P.T == Q.T >>>>>> >>>>>> On 27.05.2016 11:55, Thorsten Seitz via swift-evolution wrote: >>>>>>> We could just write >>>>>>> >>>>>>> let x: P & Q >>>>>>> instead of >>>>>>> let x: Any<P, Q> >>>>>>> >>>>>>> let x: Collection where .Element: P >>>>>>> instead of >>>>>>> let x: Any<Collection where .Element: P> >>>>>>> >>>>>>> let x: P & Q where P.T == Q.T >>>>>>> instead of >>>>>>> let x: Any<P, Q where P.T == Q.T> >>>>>>> >>>>>>> let x: P & Q & R >>>>>>> instead of >>>>>>> let x: Any<P, Q, R> >>>>>>> >>>>>>> let x: Collection >>>>>>> instead of >>>>>>> let x: Any<Collection> >>>>>>> >>>>>>> >>>>>>> This would avoid the confusion of Any<T1, T2> being something completely >>>>>>> different than a generic type (i.e. order of T1, T2 does not matter >>>>>>> whereas >>>>>>> for generic types it is essential). >>>>>>> >>>>>>> >>>>>>> -Thorsten >>>>>>> >>>>>>> >>>>>>> >>>>>>>> Am 26.05.2016 um 20:11 schrieb Adrian Zubarev via swift-evolution >>>>>>>> <[email protected] <mailto:[email protected]> >>>>>>>> <mailto:[email protected] <mailto:[email protected]>>>: >>>>>>>> >>>>>>>> Something like |type<…>| was considered at the very start of the whole >>>>>>>> discussion (in this thread >>>>>>>> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160502/016523.html >>>>>>>> >>>>>>>> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160502/016523.html>>), >>>>>>>> but it does not solve the meaning of an existential type and also might >>>>>>>> lead to even more confusion. >>>>>>>> >>>>>>>> From my perspective I wouldn’t use parentheses here because it looks >>>>>>>> more >>>>>>>> like an init without any label |Type.init(…)| or |Type(…)|. I could >>>>>>>> live >>>>>>>> with |Any[…]| but this doesn’t look shiny and Swifty to me. Thats only >>>>>>>> my >>>>>>>> personal view. ;) >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> -- >>>>>>>> Adrian Zubarev >>>>>>>> Sent with Airmail >>>>>>>> >>>>>>>> Am 26. Mai 2016 bei 19:48:04, Vladimir.S via swift-evolution >>>>>>>> ([email protected] <mailto:[email protected]> >>>>>>>> <mailto:[email protected] <mailto:[email protected]>>) >>>>>>>> schrieb: >>>>>>>> >>>>>>>>> Don't think {} is better here, as they also have "established meaning >>>>>>>>> in >>>>>>>>> Swift today". >>>>>>>>> >>>>>>>>> How about just Type(P1 & P2 | P3) - as IMO we can think of such >>>>>>>>> construction as "creation" of new type and `P1 & P2 | P3` could be >>>>>>>>> treated >>>>>>>>> as parameters to initializer. >>>>>>>>> >>>>>>>>> func f(t: Type(P1 & P2 | P3)) {..} >>>>>>>>> >>>>>>>>> >>>>>>>>> On 26.05.2016 20:32, L. Mihalkovic via swift-evolution wrote: >>>>>>>>> > How about something like Type{P1 & P2 | P3} the point being that >>>>>>>>> > "<...>" has an established meaning in Swift today which is not what >>>>>>>>> > is expressed in the "<P1,P2,P3>" contained inside Any<P1, P2,P3>. >>>>>>>>> > >>>>>>>>> >> On May 26, 2016, at 7:11 PM, Dave Abrahams via swift-evolution >>>>>>>>> >> <[email protected] <mailto:[email protected]> >>>>>>>>> >> <mailto:[email protected] >>>>>>>>> >> <mailto:[email protected]>>> wrote: >>>>>>>>> >> >>>>>>>>> >> >>>>>>>>> >>> on Thu May 26 2016, Adrian Zubarev <[email protected] >>>>>>>>> >>> <mailto:[email protected]> >>>>>>>>> >>> <mailto:[email protected] >>>>>>>>> >>> <mailto:[email protected]>>> wrote: >>>>>>>>> >>> >>>>>>>>> >>> There is great feedback going on here. I'd like to consider a few >>>>>>>>> >>> things here: >>>>>>>>> >>> >>>>>>>>> >>> * What if we name the whole thing `Existential<>` to sort out all >>>>>>>>> >>> confusion? >>>>>>>>> >> >>>>>>>>> >> Some of us believe that “existential” is way too theoretical a >>>>>>>>> >> word to >>>>>>>>> >> force into the official lexicon of Swift. I think “Any<...>” is >>>>>>>>> >> much >>>>>>>>> >> more conceptually accessible. >>>>>>>>> >> >>>>>>>>> >>> >>>>>>>>> >>> This would allow `typealias Any = Existential<>`. * Should >>>>>>>>> >>> `protocol A: Any<class>` replace `protocol A: class`? Or at least >>>>>>>>> >>> deprecate it. * Do we need `typealias AnyClass = Any<class>` or >>>>>>>>> >>> do we >>>>>>>>> >>> want to use any class requirement existential directly? If >>>>>>>>> >>> second, we >>>>>>>>> >>> will need to allow direct existential usage on protocols (right >>>>>>>>> >>> now we >>>>>>>>> >>> only can use typealiases as a worksround). >>>>>>>>> >> >>>>>>>>> >> -- >>>>>>>>> >> Dave >>>>>>>>> >> >>>>>>>>> >> _______________________________________________ >>>>>>>>> >> swift-evolution mailing list >>>>>>>>> >> [email protected] <mailto:[email protected]> >>>>>>>>> >> <mailto:[email protected] >>>>>>>>> >> <mailto:[email protected]>> >>>>>>>>> >> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>>>>> >> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>>>>>> > _______________________________________________ >>>>>>>>> > swift-evolution mailing list >>>>>>>>> > [email protected] <mailto:[email protected]> >>>>>>>>> > <mailto:[email protected] >>>>>>>>> > <mailto:[email protected]>> >>>>>>>>> > https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>>>>> > <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>>>>>> > >>>>>>>>> _______________________________________________ >>>>>>>>> swift-evolution mailing list >>>>>>>>> [email protected] <mailto:[email protected]> >>>>>>>>> <mailto:[email protected] <mailto:[email protected]>> >>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> swift-evolution mailing list >>>>>>>> [email protected] <mailto:[email protected]> >>>>>>>> <mailto:[email protected] <mailto:[email protected]>> >>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> swift-evolution mailing list >>>>>>> [email protected] <mailto:[email protected]> >>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>>>> _______________________________________________ >>>>> swift-evolution mailing list >>>>> [email protected] <mailto:[email protected]> >>>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>> _______________________________________________ >>> swift-evolution mailing list >>> [email protected] <mailto:[email protected]> >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> <https://lists.swift.org/mailman/listinfo/swift-evolution>
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