[swift-evolution] Proposal: Change of syntax for class protocols

[Austin Zheng]

I prefer the original syntax. It's easier to parse at a glance that the reference is a protocol and emphasizes the primacy of the protocol, with 'class' being a modifier on the type. I do think, though, that "protocol P : class" is inconsistent with Joe's proposed "typealias TA : class" or "func<T : class>", as the list of things following "protocol P" isn't a constraint like the other two examples. So I could see a compelling reason for going either way.

Austin


> On Dec 7, 2015, at 11:36 AM, Riley Testut via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Yes, whenever I implement the delegate pattern, I have to make sure the protocol is a class protocol so I can use a weak reference. 
> 
> While I use protocols for far more than just delegation, for the newer developers coming to Swift from Objective-C, the delegation pattern probably remains the most common use of protocols, so I agree we should make it as simple to use/understand as possible. +1 for the proposed syntax.
> 
>> On Dec 7, 2015, at 9:20 AM, Matthew Cheok via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> I would expect this to be somewhat common for building weakly referenced delegates without @objc. Shouldn't this be more common in practice?
>> 
>> On Mon, Dec 7, 2015 at 8:51 AM, Stephen Celis <stephen.celis at gmail.com <mailto:stephen.celis at gmail.com>> wrote:
>> Do others find themselves implementing class-only protocols often? They seem to be the exception, rather than the rule, to me.
>> 
>> Stephen
>> 
>> On Mon, Dec 7, 2015 at 11:32 AM, Sean Heber via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> I found this odd, too. I don’t know what kind of parsing ramifications this might have, but I like the idea. I suppose one downside is that it makes protocols for classes seem somehow special or different from other protocols - but then again, they kind of are!
>> 
>> l8r
>> Sean
>> 
>> 
>> > On Dec 7, 2015, at 10:00 AM, Matthew Cheok via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> >
>> > Currently, we declare class protocols with the following syntax:
>> >
>> > protocol TestProtocol: class, OtherProtocol {}
>> >
>> > This is odd for a few reasons:
>> > 1) The keyword class exists in the middle of the declaration
>> > 2) The keyword class follows the colon and looks a lot like inheritance
>> > 3) The keyword class occupies a somewhat arbitrary first position after the colon (otherwise we have an error)
>> >
>> > We also have another use of the class keyword as a modifier when declaring class methods:
>> >
>> > class func doSomething() {}
>> >
>> > I’m suggesting a change of syntax that rectifies the above issues:
>> >
>> > class protocol TestProtocol: OtherProtocol {}
>> >
>> > Would love to hear other thoughts on this.
>> >
>> > - Matthew
>> >
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