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

David Hart david at hartbit.com
Wed Mar 1 00:39:24 CST 2017


> On 28 Feb 2017, at 22:53, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 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’).

Could generic specialisation be disallowed in constraints? I need to think about this.

> Jordan
> 
>> On Feb 28, 2017, at 13:20, Joe Groff via swift-evolution <swift-evolution at swift.org <mailto: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
>>> 
>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
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>>> 
>>> Proposal link:
>>> 
>>> https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md
>>> Reply text
>>> 
>>> Other replies
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