I think that the alternatives considered section isn’t entirely correct. Even
if we had a more expressive type system, it would not be possible to make the
return value of `map` preserve the element type *while* still allowing types
like `String`, which aren’t parameterized by an element, to conform.
I think this would require two separate mapping protocols (ignore the straw man
names and syntax):
protocol Mappable: Sequence {
func map(_ transform: (Iterator.Element) -> Iterator.Element) -> Self
// could also add `mapInPlace`
}
protocol MappableFunctor: Mappable {
kind Self<Iterator.Element>
func map<T>(_ transform: (Iterator.Element) -> T) -> Self<T>
}
I think we’d also require either a way for the generic function to conform to
the non-generic signature if there exists a conforming instantiation if both
functions were to have the same name.
Also, we’d probably want a way to say that the `T` in the generic signature has
the same type constraints as the generic parameter would need to…
—
Anyway, the point is that we *could* consider adding the first protocol right
now (or more likely, add the requirement to `Sequence`) even though the second
protocol is not possible yet. Even if/when Swift’s type system can handle that,
the first protocol will still be necessary for types like `String` that cannot
conform to the second.
Cheers,
Jaden Geller
> On Apr 28, 2017, at 5:06 PM, Douglas Gregor via swift-evolution
> <[email protected]> wrote:
>
> Hello Swift community,
>
> The review of SE-0174 "Change `filter` to return an associated type" begins
> now and runs through May 3, 2017. The proposal is available here:
>
> https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md
>
> <https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md>
> Reviews are an important part of the Swift evolution process. All reviews
> should be sent to the swift-evolution mailing list at
>
> https://lists.swift.org/mailman/listinfo/swift-evolution
> <https://lists.swift.org/mailman/listinfo/swift-evolution>
> or, if you would like to keep your feedback private, directly to the review
> manager. When replying, please try to keep the proposal link at the top of
> the message:
>
> Proposal link:
>
> https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md
>
> <https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md>
> Reply text
> Other replies
> <https://github.com/apple/swift-evolution#what-goes-into-a-review-1>What
> goes into a review?
>
> The goal of the review process is to improve the proposal under review
> through constructive criticism and, eventually, determine the direction of
> Swift. When writing your review, here are some questions you might want to
> answer in your review:
>
> What is your evaluation of the proposal?
> Is the problem being addressed significant enough to warrant a change to
> Swift?
> Does this proposal fit well with the feel and direction of Swift?
> If you have used other languages or libraries with a similar feature, how do
> you feel that this proposal compares to those?
> How much effort did you put into your review? A glance, a quick reading, or
> an in-depth study?
> More information about the Swift evolution process is available at
>
> https://github.com/apple/swift-evolution/blob/master/process.md
> <https://github.com/apple/swift-evolution/blob/master/process.md>
> Thank you,
>
> -Doug Gregor
>
> Review Manager
>
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