[swift-evolution] [Review] SE-0156: Class and Subtype existentials

Jordan Rose jordan_rose at apple.com
Tue Feb 28 15:53:54 CST 2017

Nitpick: 'C<T> & P' is just 'C<T>' in this example. You'd need a refinement of 'P' to make it interesting ('C<T> & Q').


> On Feb 28, 2017, at 13:20, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
> Composing a base class and protocol requirements opens up the possibility of using the base class to constrain away a protocol's associated types, e.g.:
> protocol P { associatedtype T; func foo(_: T) }
> class C<T>: P { func foo(_: T) {}
> It'd be worth calling out explicitly whether this proposal allows `C<T> & P` to be used as an existential type, since although P has free associated types, the composition does not.
> -Joe
>> On Feb 28, 2017, at 1:11 PM, Douglas Gregor via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Hello Swift community,
>> The review of SE-0156 "Class and Subtype existentials" begins now and runs through March 7, 2017. The proposal is available here:
>> https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md <https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md>
>> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at
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>> Proposal link:
>> https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md
>> Reply text
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>> What goes into a review?
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