[swift-evolution] [Accepted] SE-0185 - Synthesizing Equatable and Hashable conformance

[Tony Allevato]

>From what I can tell the hash values of elements in a Set don't come into
play during encoding/decoding: they're merely serialized as the sequence of
their elements.
https://github.com/apple/swift/blob/2e5817ebe15b8c2fc2459e08c1d462053cbb9a99/stdlib/public/core/Codable.swift#L4073-L4097


On Wed, Aug 16, 2017 at 4:06 PM Robert Bennett via swift-evolution <
swift-evolution at swift.org> wrote:

> How do unstable hash values play with Codable? If you encode and save a
> Set, might you have problems interacting with it in the future? (This is
> more a Codable question than Hashable, but I figure I might as well ask
> here)
>
> On Aug 16, 2017, at 7:02 PM, Matthew Johnson via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> On Aug 16, 2017, at 5:59 PM, Rudolf Adamkovic via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> That's great. Thanks!
>
>
> Yes, excellent news!  I am *really* looking forward to seeing this
> proposal make it into an Xcode release!
>
>
> R+
>
> On 17 Aug 2017, at 00:46, John McCall <rjmccall at apple.com> wrote:
>
> On Aug 16, 2017, at 6:35 PM, Rudolf Adamkovič via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> This is fantastic news! Any chance of this landing in Swift 4.x instead of
> 5?
>
>
> It it likely to be available in 4.1, but not 4.0.
>
> John.
>
>
> R+
>
> On 17 Aug 2017, at 00:29, Chris Lattner via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Proposal Link:
> https://github.com/apple/swift-evolution/blob/master/proposals/0185-synthesize-equatable-hashable.md
>
> The review of SE-0185 “Synthesizing Equatable and Hashable conformance”
> ran from August 9…15, 2017. Feedback for the feature was glowingly
> positive, and the proposal is accepted.  The core team discussed the
> concerns raised in the feedback thread for the proposal.  Here are some
> rough notes (not intended to be exhaustive), but it is important to
> recognize that the proposal follows the design of the auto-synthesized
> Codable proposal, and that many of these same points were discussed when it
> came up:
>
> - The core team feels that adding compiler magic for this case is
> reasonable because it solves an important user need, and doesn’t preclude
> the introduction of a more general feature (e.g. like a macro system, or
> Rust's ‘deriving’ feature) in the future.  When/if that feature is designed
> and built, the compiler magic can be replaced with standard library magic.
>
> - The hash value of a type is not intended to be stable across rebuilds or
> other changes to the code.  It is ok to change if fields are reordered, the
> standard library changes the hash function, etc.  Tony pointed this out
> on-thread, saying:  The stdlib documentation for hashValue states "Hash
> values are not guaranteed to be equal across different executions of your
> program. Do not save hash values to use during a future execution.”
>
> - The code synthesized is meant to feel like a default implementation that
> you’re getting for free from a (constrained) extension on the protocol.
> This is why conformance to the protocol itself is all that is required, not
> something like “AutoEquatable”.
>
> Many thanks to Tony Allevato for driving forward this proposal.  The patch
> just needs final code review now - I think we’re all looking forward to
> this landing, congrats!
>
> Chris Lattner
> Review Manager
>
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