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

[David Ungar]

As long as I've been clear that the adoption of *this* proposal would transform a misspelling from a bug that the compiler catches to a bug that the compiler does not catch, I feel that my objection has been heard.

Thank you all,

- David

> On Aug 10, 2017, at 1:51 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> 
> Right. The objection raised is applicable to the overriding of any default implementation. However. _this_ proposal under review is about the synthesis of a default implementation, and we shouldn’t try to invent new syntax to address an orthogonal issue—and only partially at that.
> On Thu, Aug 10, 2017 at 14:45 Robert Bennett via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Yes, thanks! Here’s the full proposal for those interested: https://github.com/erica/swift-evolution/blob/c541f517dacc2030c987b6d60ad3d26d8ec5fa3a/proposals/XXXX-role-keywords.md <https://github.com/erica/swift-evolution/blob/c541f517dacc2030c987b6d60ad3d26d8ec5fa3a/proposals/XXXX-role-keywords.md>
> 
> I think that if we want to deal with the issue of some mistake arising from conforming to Equatable and/or Hashable, it should be through that proposal, not something specific to Equatable and Hashable. This sort of issue should not count against this Equatable/Hashable proposal.
> 
>> On Aug 10, 2017, at 3:39 PM, Chris Lattner <clattner at nondot.org <mailto:clattner at nondot.org>> wrote:
>> 
>>> 
>>> On Aug 10, 2017, at 12:24 PM, Robert Bennett via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> I could have sworn that this sort of issue came up on this list earlier this year… Someone proposed a mechanism encompassing all protocols, not just Equatable and Hashable, to handle the issue of mistakenly believing you’re overriding a default implementation. Having trouble finding it at the moment.
>> 
>> Is this what you’re thinking of?
>> https://github.com/apple/swift-evolution/pull/724 <https://github.com/apple/swift-evolution/pull/724>
>> 
>> -Chris
>> 
>> 
>> 
>>> .
>>> 
>>>> On Aug 10, 2017, at 3:09 PM, David Ungar via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> 
>>>> If I understand it, merely adding Equatable or Hashable will cause the compiler to synthesize requirements. This syntax opens up the possibility for errors:
>>>> 
>>>> struct Snort: Hashable {
>>>> static var hashValu /* NOTE MISSPELLING */ : Int { return 666 }
>>>> }
>>>> 
>>>> In the above example, the programmer meant to implement hashValue but misspelled it.
>>>> With the proposal as-is, the error could be covered up.
>>>> 
>>>> I would prefer to see a different syntax than merely adding conformance to "HashValue", in order to distinguish the two cases: explicit supplying the requirement vs synthesis.
>>>> 
>>>> Also, what if we want to extend this idea to other protocols? Perhaps some sort of modifier on the protocol name would be more orthogonal:
>>>> 
>>>> struct Foo: Synth Hashable, Equatable 
>>>> 
>>>> Would say that Hashable requirements get synthesized but Equatable ones do not.
>>>> 
>>>> Alternatively, it might be clearer, though more verbose to move the signalling inside:
>>>> 
>>>> struct Snort: Hashable {
>>>> synth hashValue
>>>> }
>>>> 
>>>> (I don't advocate this specific syntax, btw.) But it has the virtual of possibly making it clearer to read the code.
>>>> 
>>>> TL;DR: I favor the proposal but would prefer modification to make it more explicit.
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> 
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170810/199aa5f4/attachment.html>