> Am 23.05.2016 um 19:17 schrieb Matthew Johnson <[email protected]>: > >> >> On May 23, 2016, at 10:57 AM, Thorsten Seitz via swift-evolution >> <[email protected] <mailto:[email protected]>> wrote: >> >> >> >> Am 23.05.2016 um 00:18 schrieb Austin Zheng via swift-evolution >> <[email protected] <mailto:[email protected]>>: >> >>> I agree; the difference between protocols with and without associated types >>> has been an endless source of confusion for a lot of people. >>> >>> Speaking of which, for those who care I rewrote the draft proposal to >>> attempt a much more rigorous treatment of the semantics of the generalized >>> existential, including a discussion about existential type equivalence and >>> subtyping. It would be nice to see people poke holes in my logic so I can >>> patch them up. >>> https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md >>> >>> <https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md> >> I think that *all* methods should be available - at least in principle - >> with associated types >> - replaced by their upper bounds (i.e. Any if no constraints have been given >> either by the protocol definition itself or th existential) if in covariant >> position and >> - replaced by their lower bounds if in contravariant position >> >> As it is not possible to define lower bounds in Swift, the lower bounds are >> always the bottom type (called `Nothing` in Swift and not be confused with >> optionals). The bottom type has no members and therefore a method >> referencing that type cannot be called and is effectively not available. > > Called `Nothing` in Swift? Where do you get that? `func foo(s: Nothing) {}` > gives me “use of undeclared type `Nothing`”. If Swift had a bottom type > wouldn’t we be able to declare a function accepting an argument of type > `Nothing` (we could just never call it because we couldn’t construct an > argument).
oops, sorry, I had wanted to type „called `Nothing` in Scala“ :-) -Thorsten > >> >> -Thorsten >> >>> >>> Austin >>> >>>> On May 22, 2016, at 3:05 PM, Russ Bishop via swift-evolution >>>> <[email protected] <mailto:[email protected]>> wrote: >>>> >>>> >>>>> On May 17, 2016, at 1:55 PM, Joe Groff via swift-evolution >>>>> <[email protected] <mailto:[email protected]>> wrote: >>>>> >>>>> I agree with this. If we're certain we should reskin protocol<> as Any<>, >>>>> we should frontload that change—in addition to affecting source code, >>>>> it'd also influence the runtime behavior of type printing/parsing, which >>>>> can't be statically migrated in the future. I think any discussion of >>>>> extending existentials has to be considered out of scope for Swift 3, >>>>> though, so the Any rename deserves its own proposal. >>>>> >>>>> -Joe >>>> >>>> >>>> Its really unfortunate that the generics work is probably going to be >>>> deferred. When you really dive in to protocol-oriented programming and >>>> designing frameworks to be native Swift (taking advantage of Swift >>>> features) the existential problem comes up a lot and leads to sub-optimal >>>> designs, abandonment of type safety, or gobs of boilerplate. >>>> >>>> >>>> Russ >>>> >>>> _______________________________________________ >>>> 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
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