[swift-evolution] Will existentials ever conform to their protocols?

Slava Pestov spestov at apple.com
Wed Jan 18 00:50:56 CST 2017

> On Jan 17, 2017, at 9:33 PM, David Sweeris via swift-evolution <swift-evolution at swift.org> wrote:
> On Jan 17, 2017, at 22:30, Braeden Profile via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Hello Swift Community!
>> I know that I’ve seen this mentioned before, but what with Enhanced Existentials being brought up, I think this is worth mentioning now.  What is the plan regarding letting existentials conform to their protocols?  Currently, in Swift 3, it is impossible to write code like this:
>> protocol Updatable
>> 	{ func update() }
>> struct UpdatePool<T: Updatable>
>> 	{ /* ... */ }
>> let heterogenousPool = UpdatePool<Updatable>()
>> Error on the last line:  “Using ‘Updatable’ as a concrete type conforming to protocol ‘Updatable’ is not supported.”
>> Although my most common use case of this behavior has actually been solved (using ‘AnyObject’ as a concrete type conforming to ‘AnyObject’), I wonder why this can’t be extended to any protocol existential (a field which is about to explode, if we succeed in Enhancing them).
>> What do you guys think?
> +1, but I think there's a compiler limitation preventing it at the moment.

See my recent post: https://www.mail-archive.com/swift-users@swift.org/msg03427.html


> - Dave Sweeris 
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