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

David Sweeris davesweeris at mac.com
Tue Jan 17 23:33:52 CST 2017

> On Jan 17, 2017, at 22:30, Braeden Profile via swift-evolution <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.

- Dave Sweeris 
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