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

Haravikk swift-evolution at haravikk.me
Sat Aug 19 06:06:17 CDT 2017

> On 19 Aug 2017, at 11:44, Tino Heth <2th at gmx.de> wrote:
>> Am 17.08.2017 um 20:11 schrieb Haravikk via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>:
>> For me the whole point of a basic protocol is that it forces me to implement some requirements in order to conform; I can throw a bunch of protocols onto a type and know that it won't compile until I've finished it, developers get distracted, leave things unfinished to go back to later, make typos etc. etc. To me declaring a conformance is a declaration of "my type will meet the requirements for this make, sure I do it", not "please, please use some magic to do this for me"; there needs to be a clear difference between the two.
> My conclusion isn't as pessimistic as yours, but I share your objections: Mixing a normal feature (protocols) with compiler magic doesn't feel right to me — wether it's Equatable, Hashable, Codable or Error.
> It's two different concepts with a shared name*, so I think even AutoEquatable wouldn't be the right solution, and something like #Equatable would be a much better indicator for what is happening.
> Besides that specific concern, I can't fight the feeling that the evolution process doesn't work well for proposals like this:
> It's a feature that many people just want to have as soon as possible, and concerns regarding the long-term effects are more or less washed away with eagerness.
> - Tino
> * for the same reason, I have big concerns whenever someone proposes to blur the line between tuples and arrays

Agreed. To be clear though; in spite of my pessimism this is a feature that I do want, but I would rather not have it at all than have it implemented in a way that hides bugs and sets a horrible precedent for the future.

I realise I may seem to be overreacting, but I really do feel that strongly about what I fully believe is a mistake. I understand people's enthusiasm for the feature, I do; I hate boilerplate as much as the next developer, but as you say, it's not a reason to rush forward, especially when this is not something that can be easily changed later.

That's a big part of the problem; the decisions here are not just about trimming boilerplate for Equatable/Hashable, it's also about the potential overreach of every synthesised feature now and in the future as well.
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