[swift-evolution] [PROPOSAL]Return subclass type to a protocol where a superclass is defined without the need for associatedtype

Gwendal Roué gwendal.roue at gmail.com
Mon Apr 18 05:11:36 CDT 2016

> Le 18 avr. 2016 à 12:01, Yogev Sitton <yogev.sitton at gmail.com> a écrit :
> I’m referring you to Ross O’Brien’s post:
> As of Swift 2.2, if a variable has a closure type of e.g. () -> Shape, a closure of type () -> Circle would be considered a match.  If a class implements 'func make() -> Shape', a subclass implementing 'func make() -> Circle' has to override. However, if a protocol requires a 'func make() -> Shape', a type implementing 'func make() -> Circle' isn't considered to be conforming. That does seem strange.
> Protocols behaves differently than closures and classes and I think they should behave the same.

All right, I get it.

Shape, as a return type, is "trampoline" data that wraps any Shape value, when Circle is just a Circle. That's why the two functions () -> Shape? and () -> Circle? don't match today.

But maybe they will eventually, thanks to your request!


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