[swift-evolution] [Pitch] Requiring proactive overrides for default protocol implementations.
Wallacy
wallacyf at gmail.com
Thu Apr 28 09:11:59 CDT 2016
I wrote a proposal few weeks ago about "Complete Composition Model" in
Swift, but still not finish (too many details)...
In my proposal, i thought about the problem in this topic. However after
thinking more generally, I found it best to solve in other direction:
- Every time one default protocol implementations is provide, the generated
Header will include de "default" at beginner.
-- No source code change, the change is just for generated header. For
Frameworks and libs, will apear em the "final generated header" of course.
But for changes in our own module, will apear on xcode generated header,
auto complete, detail tab, changes in color code, etc...
The ideia is provide a way to "see" more easily if a method has a default
implementation, but does not change de code itself because this
implementation can be made any time by someone, without break anything.
- Every time we "re implement" one default protocol implementation for
other module with already have this "default" keyword, we need to provide a
"implements" (or require) keyword to avoid a compiler warning.
-- Do not put a keyword to tell if you are implementing a protocol
requirement is not exactly a error, but can be considered if you previously
know about default implementation. No keyword is needed if no default
implementations is provided, but can be used for clarify the intention.
- For or own module, xcode / auto-complete, detail tab, color code, etc...
can tel you about the "has default implementation" without the warning.
At end of the day, there no need to any noise to tell something about
default implementation, just a little help.
If we make "everything explicit", inference type will be abolished.
Sometimes we can count on to develop "look the metadatas/interfaces"
If someone wants I can post the proposal I have written tomorrow.
Em qui, 28 de abr de 2016 às 02:08, Charles Srstka via swift-evolution <
swift-evolution at swift.org> escreveu:
> I would prefer the “override” only apply to methods that already had
> default protocol implementations, because then it could help avoid the
> mistake of overriding a default implementation that you didn’t realize was
> there, thinking that this was a method that you needed to supply.
>
> Charles
>
> On Apr 27, 2016, at 8:26 PM, Howard Lovatt via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> @Tod,
>
> This was a concern when Java changed the behaviour of `@Override`, but it
> didn't pan out. Everyone, even those with reservations, grew to like the
> new behaviour. I think the much improved error messages from the compiler
> helped, e.g.:
>
> protocol ViewObserver {
> func append(observer observer: Observer)
> func remove(observer observer: Observer)
> func removeAll()
> }
> struct AViewObserver: ViewObserver {
> func apend(observer observer: Observer) {
> ...
> }
> func remove(observer observer: Observer) {
> ...
> }
> func removeAll() {
> ...
> }
> }
>
> The only error you get at present with the above is that `AViewObserver`
> does not conform to `ViewObserver`, it doesn't tell you why. With the
> change the compiler would highlight that `apend` doesn't override `append`
> :(.
>
>
> -- Howard.
>
> On 28 April 2016 at 11:17, Tod Cunningham <tcunningham at vectorform.com>
> wrote:
>
>> I think it would be odd and confusing to always have to use override when
>> implementing protocol methods (especially protocol methods without default
>> implementations). To me override is telling me that there is another
>> implementation, and I am for lack of a better word overriding that
>> implementation. However, for a protocol w/o a default implementation,
>> there is no implementation. You aren’t overriding anything. You are just
>> conforming to a signature. Now protocol’s with default implementations
>> there could be a case made for using override. Expect Swift current
>> implementation doesn't really override the default implementation, as shown
>> in my example. The other issues would be if I am overriding something, I
>> would expect to be able to execute the default implementation from within
>> my override.
>>
>> It might be nice to have some syntax that would identify the protocol
>> that is being implemented at the point of the implementation. For example
>> (although I don't like this syntax):
>> func (protocolname1, protocolname2) commonmethod() -> Void { .. the
>> implementation.. }
>>
>> - Tod Cunningham
>> ________________________________________
>> From: swift-evolution-bounces at swift.org <
>> swift-evolution-bounces at swift.org> on behalf of Josh Parmenter via
>> swift-evolution <swift-evolution at swift.org>
>> Sent: Wednesday, April 27, 2016 8:27 PM
>> To: Howard Lovatt
>> Cc: swift-evolution
>> Subject: Re: [swift-evolution] [Pitch] Requiring proactive overrides for
>> default protocol implementations.
>>
>> On Apr 27, 2016, at 17:23, Howard Lovatt via swift-evolution <
>> swift-evolution at swift.org<mailto:swift-evolution at swift.org>> wrote:
>>
>> I think that you should *always* have to write `override` when
>> implementing a protocol method, you can think of this as override an
>> abstract declaration. In particular I think the following should be
>> enforced:
>>
>> protocol A { func a() }
>> extension A { override func a() { ... } }
>> struct AnA: A { override func a() { ... } }
>>
>> protocol B { func b() }
>> struct AB: B { override func b() { ... } }
>>
>>
>> I'm rather new to the list - but I would like to say that I agree with
>> this. I think it gives clarity both to code readability, and for learning
>> the language.
>> Best
>> Josh
>>
>> I think this change will work out well since it mimics what happened in
>> Java, originally the Java annotation `@Override` was used much like
>> `override` is currently used in Swift. However it was problematic and was
>> changed so that you always add the annotation, as shown above (in the Swift
>> context). One of the big advantages of this change is that the error
>> messages are much better (this was very noticeable in Java).
>>
>> This proposal has come up before on swift-evolution, so it obviously has
>> some support.
>>
>> On Thursday, 28 April 2016, Erica Sadun via swift-evolution <
>> swift-evolution at swift.org<mailto:swift-evolution at swift.org>> wrote:
>> From the Swift Programming Language: Methods on a subclass that override
>> the superclass's implementation are marked with override-overriding a
>> method by accident, without override, is detected by the compiler as an
>> error. The compiler also detects methods with override that don't actually
>> override any method in the superclass.
>>
>> I would like to extend this cautious approach to protocols, forcing the
>> developer to deliberately override an implementation that's inherited from
>> a protocol extension. This would prevent accidental overrides and force the
>> user to proactively choose to implement a version of a protocol member that
>> already exists in the protocol extension.
>>
>> I envision this as using the same `override` keyword that's used in class
>> based inheritance but extend it to protocol inheritance:
>>
>> protocol A {
>> func foo()
>> }
>>
>> extension A {
>> func foo() { .. default implementation ... }
>> }
>>
>> type B: A {
>>
>> override required func foo () { ... overrides implementation ... }
>> }
>>
>>
>> I'd also like to bring up two related topics, although they probably
>> should at some point move to their own thread if they have any legs:
>>
>> Related topic 1: How should a consumer handle a situation where two
>> unrelated protocols both require the same member and offer different
>> default implementations. Can they specify which implementation to accept or
>> somehow run both?
>>
>> type B: A, C {
>> override required func foo() { A.foo(); C.foo() }
>> }
>>
>> Related topic 2: How can a consumer "inherit" the behavior of the default
>> implementation (like calling super.foo() in classes) and then extend that
>> behavior further. This is a bit similar to how the initialization chaining
>> works. I'd like to be able to call A.foo() and then add custom follow-on
>> behavior rather than entirely replacing the behavior.
>>
>> type B: A {
>> override required func foo() { A.foo(); ... my custom behavior ... }
>> }
>>
>> cc'ing in Jordan who suggested a new thread on this and Doug, who has
>> already expressed some objections so I want him to have the opportunity to
>> bring that discussion here.
>>
>> - E
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org<mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160428/f8ce871a/attachment.html>
More information about the swift-evolution
mailing list