[swift-evolution] Overriding specific methods when adopting protocols with extension

[Björn Forster]

Hi Brian,
is the override proposal still in the making?

Kind Regards,
Björn

On Thu, Mar 23, 2017 at 4:24 PM, Brian King via swift-evolution <
swift-evolution at swift.org> wrote:

> Hey Iman, This is a known bug SR-103. It certainly has caught a few people
> off guard. Dale Buckley is working on an evolution proposal that would
> allow the bug to be fixed:
>
> Proposal:
> https://gist.github.com/dlbuckley/1858a7c0b5c027248fe16171d23ba01d
>
> Conversation on the Proposal:
> https://lists.swift.org/pipermail/swift-evolution/
> Week-of-Mon-20170313/033787.html
>
> The only work around at this time is to make sure that your base class
> implements all methods in the protocol.
>
> Brian King
>
>
> On Thu, Mar 23, 2017 at 11:15 AM, Iman Zarrabian via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Hi,
>> This is my first contribution to this list so I’m a little nervous.
>> I’ve been refactoring some code in one of our internal frameworks and
>> noticed something I didn’t noticed about protocols before.
>> Maybe I’m missing the big picture here but I’ll expose the issue to you
>> anyway.
>> Consider these protocols and classes declarations :
>>
>> protocol Foo {
>>     func bar()
>>     func specificBar()
>>     func moreBar()
>> }
>>
>> extension Foo {
>>     func specificBar() {
>>         print("default specificBar implementation")
>>     }
>> }
>>
>> extension UIView: Foo {
>>     func bar() {
>>         print("uiview default bar")
>>         specificBar()
>>         moreBar()
>>     }
>>
>>
>>     func moreBar() {
>>         print("UIView is foo compliant and implements moreBar function")
>>     }
>> }
>>
>> class CustomView: UIView {
>>     func startJob() {
>>         bar()
>>     }
>>
>>
>>     func specificBar() {
>>         print("CustomView specific bar implementation")  //This is the
>> implementation I want for specificBar but this is not the one picked at
>> runtime.
>>     }
>> }
>>
>>
>> let view = CustomView()
>> view.startJob()
>>
>> //Prints :
>> //uiview default bar
>> *//default specificBar implementation*
>> //UIView is foo compliant and implements moreBar function
>>
>> I was wondering if it is a good idea to give the CustomView class the
>> power to be more specific about it’s parent protocol adoption.
>>
>> It seems to me that implementation of a protocol method cannot be easily
>> changed by subclasses of the class that actually adopts the protocol in the
>> first place. IMO one way to achieve the kind of specialization I’m trying
>> to do is to create two protocols and another would be to implement a
>> version of specificBar in the superclass (UIView here)
>>
>> But does it make sense to consider some kind of cherry picking (with a
>> new keyword) for those methods we want to implement more precisely than the
>> one provided on the protocol extension?
>> Consider this new code for CustomView :
>>
>> class CustomView: UIView {
>>     func startJob() {
>>         bar()
>>     }
>>
>>
>>     override adoption func specificBar() {  //or override protocol =>
>> implements a method from a protocol adopted by the superclass
>>         print("CustomView specificBar implementation")
>>     }
>> }
>>
>> let view = CustomView()
>> view.startJob()
>>
>> //Would print :
>> //uiview default bar
>> *//CustomView specificBar implementation*
>> //UIView is foo compliant and implements moreBar function
>>
>> I would appreciate your feedback.
>>
>> --
>> Iman Zarrabian
>> @imanzarrabian
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>
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