On Mon, May 9, 2016 at 2:33 AM, David Hart <[email protected]> wrote:
> > On 09 May 2016, at 09:30, Xiaodi Wu <[email protected]> wrote: > > Great, I hope this proposal finds much success with the community. > > One more thing: your title makes mention of protocol extensions, but > protocol extensions are mentioned nowhere else. Please include details on > typealiases in protocol extensions within the text or remove it altogether > from the proposal. > > > I left it in for now because it was explicitly mentioned in the Generics > Manifesto (the title is a simple copy and paste), but I have yet to find > good examples to illustrate their usefulness. Perhaps you could help me out > on this one? > Nothing's coming to mind right off the bat. Perhaps the writer of the Manifesto could chime in... On Mon, May 9, 2016 at 02:24 David Hart <[email protected]> wrote: > >> On 09 May 2016, at 08:53, Xiaodi Wu <[email protected]> wrote: >> >> And to clarify, FWIW, I think it'd be wonderful to implement this >> feature, and I share your sense that sometimes conversations on this list >> get a little sidetracked. My comments are not meant to suggest that this is >> not a good feature; rather, they go to your question to the list--does your >> proposal need any modifications before a PR? >> >> IMO, some sections need to be fleshed out. Some discussion on how your >> proposed rules interact with other aspects of the language when they are >> used in the daily task of conforming types to protocols is called for. I >> accept your point that perhaps it doesn't belong in the 'Impact on Existing >> Code' section. >> >> >> I’ll add something. >> >> I hope you'll forgive me for saying that the proposal seems, overall, >> hastily written. That there are two misspelled instances of "typealias" in >> a proposal about typealias does not give one confidence that what is >> proposed has been sufficiently considered. >> >> >> I don’t mind you saying it, it is a very early draft. That’s why I’m >> putting it in front of the community before sending it for a Pull Request. >> >> On Mon, May 9, 2016 at 01:06 Xiaodi Wu <[email protected]> wrote: >> >>> I see your point that nothing breaks in the stdlib with your proposal >>> alone. It's undeniably true--by construction!--that a purely additive >>> feature, if never used, will not cause problems. >>> >>> That said, since the time that this feature was outlined in Doug's >>> manifesto, I have been wondering how clashes such as the examples in my >>> previous email are to be handled--i.e. what the rules of the language are >>> to be--which I think is certainly germane to your proposal. Can a >>> conforming type override a protocol typealias? Can a type conform to two >>> protocols with conflicting typealiases if all requirements are otherwise >>> satisfied? Surely, these merit discussion in your proposal. >>> >>> On Mon, May 9, 2016 at 12:48 AM David Hart <[email protected]> wrote: >>> >>>> Hello Xiaodi, >>>> >>>> What I mean by there is no impact on existing code is that the language >>>> change has no impact. Of course, if the Standard Library then declares a >>>> typealias Element in Sequence, it will clash with code which has declared >>>> an Element typealias in sub-protocols, but that is separate from the >>>> proposal. >>>> >>>> On 09 May 2016, at 07:28, Xiaodi Wu <[email protected]> wrote: >>>> >>>> If the protocol Sequence has typealias Element, does that mean I also >>>> have MyConformingSequence.Element? >>>> >>>> If so, I think there is a potential impact on existing code not >>>> mentioned. Suppose MyConformingSequence already (unwisely) declares >>>> typealias Element. Now, what happens when I try to migrate my code to your >>>> proposed version of Swift? >>>> >>>> This is a toy example, of course. More generally, though, I wonder >>>> about this question: >>>> >>>> Suppose two protocols A and B each declare typealias Element. These >>>> typealiases are, as you proposed, intended to simplify referencing indirect >>>> associated types. But are they themselves considered protocol requirements? >>>> >>>> I ask because, suppose I want to conform type T to A and B. I implement >>>> all the required methods and properties for such conformance. I declare the >>>> appropriate typealiases for the associatedtypes declared in both protocols. >>>> But, if A.Element and B.Element are incompatible with each other, it is >>>> nonetheless impossible to conform T to both A and B? If it's forbidden, >>>> isn't that kind of a bummer, since what's getting in the way is a naming >>>> clash arising from a facility intended to simplify the naming of things >>>> rather than provide for new functionality? If it's permitted, what is >>>> T.Element? Some clarity here would be nice. >>>> On Sun, May 8, 2016 at 6:17 PM David Hart via swift-evolution < >>>> [email protected]> wrote: >>>> >>>>> Hello, >>>>> >>>>> I’ve come again with another proposal directly from the Generics >>>>> Manifesto. Please let me know if it needs any modifications before sending >>>>> the pull request. >>>>> >>>>> Typealiases in protocols and protocol extensions >>>>> >>>>> - Proposal: SE-XXXX >>>>> >>>>> <https://github.com/hartbit/swift-evolution/blob/typealiases-in-protocols/proposals/XXXX-typealiases-in-protocols.md> >>>>> - Authors: David Hart <https://github.com/hartbit>, Doug Gregor >>>>> <https://github.com/DougGregor> >>>>> - Status: TBD >>>>> - Review manager: TBD >>>>> >>>>> >>>>> <https://github.com/hartbit/swift-evolution/blob/typealiases-in-protocols/proposals/XXXX-typealiases-in-protocols.md#introduction> >>>>> Introduction >>>>> >>>>> This proposal is from the Generics Manifesto >>>>> <https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md> and >>>>> brings the typealias keyword back into protocols for type aliasing. >>>>> >>>>> <https://github.com/hartbit/swift-evolution/blob/typealiases-in-protocols/proposals/XXXX-typealiases-in-protocols.md#motivation> >>>>> Motivation >>>>> >>>>> In Swift versions prior to 2.2, the typelias keyword was used outside >>>>> of protocols to declare type aliases and in protocols to declare >>>>> associated >>>>> types. Since SE-0011 >>>>> <https://github.com/apple/swift-evolution/blob/master/proposals/0011-replace-typealias-associated.md> >>>>> and >>>>> Swift 2.2, associated type now use the associatedtype keyword and >>>>> typelias is available for implementing true associated type aliases. >>>>> >>>>> <https://github.com/hartbit/swift-evolution/blob/typealiases-in-protocols/proposals/XXXX-typealiases-in-protocols.md#proposed-solution>Proposed >>>>> solution >>>>> >>>>> The solution allows the creation of associated type aliases. Here is >>>>> an example from the standard library: >>>>> >>>>> protocol Sequence { >>>>> associatedtype Iterator : IteratorProtocol >>>>> typealias Element = Iterator.Element >>>>> } >>>>> >>>>> The example above shows how this simplifies referencing indirect >>>>> associated types: >>>>> >>>>> func sum<T: Sequence where T.Element == Int>(sequence: T) -> Int { >>>>> return sequence.reduce(0, combine: +) >>>>> } >>>>> >>>>> >>>>> <https://github.com/hartbit/swift-evolution/blob/typealiases-in-protocols/proposals/XXXX-typealiases-in-protocols.md#detailed-design>Detailed >>>>> design >>>>> >>>>> The following grammar rules needs to be added: >>>>> >>>>> *protocol-member-declaration* → *protocol-typealias-declaration* >>>>> >>>>> *protocol-typealias-declaration* → *typealias-declaration* >>>>> >>>>> <https://github.com/hartbit/swift-evolution/blob/typealiases-in-protocols/proposals/XXXX-typealiases-in-protocols.md#impact-on-existing-code>Impact >>>>> on existing code >>>>> This will have no impact on existing code, but will probably require >>>>> improving the Fix-It that was created for migrating typealias to >>>>> associatedtype in Swift 2.2. >>>>> _______________________________________________ >>>>> 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
