> On Aug 9, 2017, at 4:09 PM, Chris Lattner <clatt...@nondot.org> wrote:
>
> Hello Swift community,
>
> The review of SE-0185 - "Synthesizing Equatable and Hashable conformance"
> begins now and runs through August 15, 2017. The proposal is available here:
> https://github.com/apple/swift-evolution/blob/master/proposals/0185-synthesize-equatable-hashable.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
>
> 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:
>
> 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?
+1, it addresses one of the biggest pain points that cause people to reach for
metaprogramming facilities.
I have one clarifying point and tweak. The proposal states:
> A struct T: Hashable that satisfies the conditions above will receive a
> synthesized implementation of var hashValue: Int { get } that uses an
> unspecified hash function† to compute the hash value by incorporating the
> hash values of the fields as its terms, in definition order.
This means that if the hash-combine operation is not commutative, then
hashValues are not stable modulo member reordering. Was this scenario
explicitly thought through? I don’t think it’s likely to be an issue in
practice, but it's an artifact of implicit and ordered member-wise synthesis.
It’s not obvious that declaration order is clearly the best order, e.g.
declaration order is not necessarily memory-layout order. It might be better to
leave the precise order unspecified, so long as it's guaranteed consistent
during the execution of a program.
> • 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?
It's a reasonably scoped chunk of functionality for the biggest pain points, so
yes.
> • If you have used other languages or libraries with a similar feature,
> how do you feel that this proposal compares to those?
Haskell and Rust both have “deriving" constructs for generating these kinds of
things, and that simplifies a lot of code.
> • How much effort did you put into your review? A glance, a quick
> reading, or an in-depth study?
>
Thought about it a bit; read it quickly.
> More information about the Swift evolution process is available at:
> https://github.com/apple/swift-evolution/blob/master/process.md
>
>
> Thank you,
>
> Chris Lattner
> Review Manager
>
>
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