> On Feb 21, 2017, at 10:53 PM, David Hart via swift-evolution 
> <swift-evolution@swift.org> wrote:
> 
> Hello list,
> 
> Found out yesterday that you can’t extend all existentials in Swift:
> 
> protocol P1 {}
> extension P1 {}
> // works as expected
> 
> protocol P2 {}
> extension P1 & P2 {}
> // error: non-nominal type 'P1 & P2' cannot be extended

This will make name lookup rather complicated. I’d rather not do it. As Jacob 
mentions, you can almost simulate it with a constrained extension.

> 
> extension Any {}
> // error: non-nominal type 'Any' cannot be extended
> 
> extension AnyObject {}
> // error: 'AnyObject' protocol cannot be extended

These two are by design. In the future, AnyObject will be ‘special’ (basically 
we want to model it as ‘Any & class’), and not a protocol.

Slava

> 
> I’d like to write a proposal to lift some of those restrictions. But the 
> question is: which should be lifted? P1 & P2 seems like an obvious case. But 
> what about Any and AnyObject? Is there a design reason that we shouldn’t 
> allow it?
> 
> David.
> _______________________________________________
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

Reply via email to