[swift-evolution] [Review] SE-0131: Add AnyHashable to the standard library
pyry.jahkola at iki.fi
Mon Jul 25 15:34:07 CDT 2016
> On 24 Jul 2016, at 01:26, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
> Hello Swift community,
> The review of "SE-0131: Add AnyHashable to the standard library" begins now and runs through July 25. This proposal is a bit unusual, since it is a late additive proposal. The reason we need to do something here is as a critical part of "SE-0116: Import Objective-C id as Swift Any type”, enabling importing untyped NSDictionary's and NSSet’s properly. The core team considers this already conceptually approved for Swift 3 as part of SE-0116, but would greatly appreciate feedback on the details of the proposed design.
> The proposal is available here:
> * What is your evaluation of the proposal?
+1, this is a nice addition, and useful at times.
There's one very obscure gotcha <https://swiftlang.ng.bluemix.net/#/repl/c1ddd24113169ab82df118660c8e0de6ea24e48d32997c327638a88dc686e91f> with AnyHashable that subclass instances of a Hashable base class should be cast to the base type before wrapping into AnyHashable, otherwise such wrapped values may break the equivalence law of symmetry (`a == b` iff `b == a`).
But now that most of Foundation's class clusters are bridged into value types, that problem is unlikely to occur to anyone anymore.
> * Is the problem being addressed significant enough to warrant a change to Swift?
So and so.
> * Does this proposal fit well with the feel and direction of Swift?
Yes. Maybe it will also help us gain more experience when designing real existential types.
> * If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
A bit of a hack compared to real existentials. But a good one.
> * How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
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