[swift-evolution] Enhanced Existentials

[David Hart]

> On 8 Jan 2017, at 06:17, Douglas Gregor via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
> 
> Sent from my iPhone
> 
>> On Jan 6, 2017, at 11:04 PM, Russ Bishop <xenadu at gmail.com> wrote:
>> 
>> 
>>> On Jan 4, 2017, at 8:48 PM, Douglas Gregor via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> 
>>>> 
>>>> Would love to see this come forward into discussion.
>>> 
>>> Yeah. I'm less sure about the other enhancements to existentials fitting into Swift 4, e.g., the creation of existentials for protocols with associated types. Although important, it's a big feature that will take a bunch of design and implementation time, and I'm leery of accepting something that we might not actually be able to achieve. 
>>> 
>>> - Doug
>> 
>> By this are you referring to generalized existentials?
> 
> Yes. I actually prefer the term "generalized existentials".
> 
>> If so I’ll say this is such a constant pain point and perverts so many API designs… not to mention vomiting AnyXYZ type-erased wrappers everywhere… In my completely non-authoritative personal opinion we shouldn’t ship Swift 4 without it :)
> 
> To be absolutely clear, I think this is an extremely important feature. It's also a significant undertaking in both design and implementation. 

Hasn't most of the design work already been done by Austin and all those participating back then? What is missing? How much of the original proposal is possible to implement in the Swift 4 (on top of Superclass + Protocol)? Just want some hints on how to drive this so we can get as much of generalized existentials for Swift 4.

>  - Doug
> 
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