[swift-evolution] [Review] SE-0161: Smart KeyPaths: Better Key-Value Coding for Swift

[Karl Wagner]

> What is your evaluation of the proposal?
+1

> Is the problem being addressed significant enough to warrant a change to Swift?
Yes

> Does this proposal fit well with the feel and direction of Swift?
Yes

> If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
Lots of languages have key-paths, but usually they are strings. This adds some type-safety, so that’s nice.

> How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
A quick reading. I also have a couple of questions:

1) Can we get keypaths from protocol existentials?

protocol MyProto {
    var something: Int { get }
}
struct MyThing: MyProto { /* … */ }

let myProtoSomethingKeypath = #keypath(MyProto, .something)
let value: Int = MyThing()[keypath: myProtoSomethingKeypath]  // seems reasonable, right?

2) What about if it has associated types?

let secondElement = #keypath(Collection, .subscript[1])  // if Collection.Iterator.Element had constraints, could we dig in to the instance?

let _: Int = [1,2,3][keypath: secondElement]
let _: String = [“a”, “b”, “c”][keypath: secondElement]


But I’d still +1 the proposal even if was limited to concrete types.

Also, that brings me to 2 related comments regarding the evolution of the feature:

1) It would be nice to allow keypaths of constrained protocol existentials

    let secondElementFirstCharacter = #keypath(Collection where Iterator.Element == String, .subscript[0].characters.first)

2) It would be nice to be able to get keypaths to members which we don’t know exist. Members and protocol conformances may be retroactively added by 3rd-party code.

And that’s all.

- Karl

> On 30 Mar 2017, at 18:25, Douglas Gregor via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hello Swift community,
> 
> The review of SE-0161 "Smart KeyPaths: Better Key-Value Coding for Swift" begins now and runs through April 5, 2017. The proposal is available here:
> 
> https://github.com/apple/swift-evolution/blob/master/proposals/0161-key-paths.md <https://github.com/apple/swift-evolution/blob/master/proposals/0161-key-paths.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/0161-key-paths.md <https://github.com/apple/swift-evolution/blob/master/proposals/0161-key-paths.md>
> Reply text
> Other replies
>  <https://github.com/apple/swift-evolution/pulls#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
> 
> Review Manager
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170330/f7a1d161/attachment.html>