[swift-evolution] [Review #2] SE-0161: Smart KeyPaths: Better Key-Value Coding for Swift

[Brent Royal-Gordon]

> 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?
I don't adore the `\` syntax because I don't quite see the underlying logic of that symbol, but it's a *massive* improvement over the old `#keyPath(Type, .path)` mess, and in all other respects I remain extremely positive on this proposal.

It's worth noting that, if you write `\Person.name.valueType`, this syntax is ambiguous—it could mean "make a key path for the `valueType` property on `name` property of `Person`", or it could mean "make a key path for the `name` property of `Person`, then access the key path's `valueType` property". We can solve this by always interpreting it as the former and requiring parentheses for the latter—that is, `(\Person.name).valueType`—but I thought it was worth calling out explicitly.

> 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?
Pretty much.

> If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
Just Objective-C. This is much better.

> How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
Quick reading of this revision.

-- 
Brent Royal-Gordon
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