[swift-evolution] [Discussion] Allowing extending existentials

[Douglas Gregor]

> On Feb 21, 2017, at 11:46 PM, Slava Pestov <spestov at apple.com> wrote:
> 
>> 
>> On Feb 21, 2017, at 11:42 PM, David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> If we drop the idea of extending Any and AnyObject (which is out of scope), does the fact that what is left is syntactic sugar make it unsuitable for Swift 4? I remember Chris saying syntactic sugar is not the goal for Swift 4, but this syntactic sugar looks really sweet (pun intended).
>> 
> 
> It’s unlikely we’ll make it a priority to implement anything like that in the Swift 4 timeframe, but PRs are more than welcome ;-)

Part of the reason that Swift 4 stage 2 doesn’t encourage “pure sugar” proposals is because it saps implementation bandwidth for model-enhancing or model-breaking changes that have much more effect. The actual effect is that we can end up reviewing a bunch of proposals that will not get implemented. Having an actual implementation ready to go prior to review can change that calculus somewhat—that’s why, for example, smallish “pure" standard library proposals are in scope but should have implementations [*].

	- Doug


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