[swift-evolution] [Discussion] Enforcing Calling Super

[Vanderlei Martinelli]

I vote (again) to only specify if a func requires super. When to call super
is up to the developer after reading the docs.

-Van

On Thu, Feb 25, 2016 at 5:02 PM, Jean-Daniel Dupas via swift-evolution <
swift-evolution at swift.org> wrote:

>
> Le 25 févr. 2016 à 20:28, Matthew Johnson <matthew at anandabits.com> a
> écrit :
>
>
> On Feb 25, 2016, at 1:23 PM, Jean-Daniel Dupas <mailing at xenonium.com>
> wrote:
>
>
> Le 25 févr. 2016 à 20:19, Matthew Johnson via swift-evolution <
> swift-evolution at swift.org> a écrit :
>
>
>
> Sent from my iPad
>
> On Feb 25, 2016, at 1:17 PM, Jean-Daniel Dupas via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> Le 25 févr. 2016 à 16:47, Jeremy Pereira via swift-evolution <
> swift-evolution at swift.org> a écrit :
>
>
> On 17 Feb 2016, at 22:26, Kyle Sherman via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Thanks for the replies.
>
> Kenny: After thinking about it more, discussing with Peter, and looking
> Haravikk’s comments, I think the best thing would be for this to be a
> warning as suggested. I respectfully disagree that as a library creator you
> would not be able to know that a call to super should be required.
>
>
> I disagree. You can’t possibly know all the use-cases in which your class
> might be subclassed.
>
> In particular, it is absurd to enforce having the call to super as the
> first or last line of the method. That would stop me doing things like this:
>
> override func viewDidLoad()
> {
>     print(“About to run super.viewDidLoad()”)
>     super.viewDidLoad()
>     print(“Finished super.viewDidLoad()”)
> }
>
> Then there’s the perfectly reasonable case like this:
>
> override func viewDidLoad()
> {
>     functionThatCallsSuperViewDidLoad()
> }
>
> Why shouldn’t I be allowed to do that?
>
>
> +1 with your concern. I’d be curious to see a single real world use case
> where enforcing first or last is required.
>
>
> I posted several examples from Apple frameworks in an old thread about
> this.  You might want to look for that message in the archives.
>
>
> And not a single one has a strong requirement about prohibiting code to be
> call before or after the super class implementation.
>
>
> It depends what you mean by “strong”.  Sure, a log statement won’t make
> much difference.  But the examples I gave do have semantic requirements
> that super should either go first or last in performing real work to be
> done by the method.
>
>
> For instance:
>
> // If you override this method, you must call super first to get the invalidation context object to return. After getting this object, set any custom properties and return it.
> func invalidationContextForBoundsChange(_ newBounds: CGRect) -> UICollectionViewLayoutInvalidationContext
>
>
> Why must I call super first ? Why can’t I don’t a bunch of things that are
> related to my subclass first ?
>
> How am I supposed to do if I want to compute a new bound to pass to super
> instead of forwarding it naively.
>
> ditto for
>
> // call super first to retrieve the item’s existing attributes and then make your changes to the returned structure.
> layoutAttributesForInteractivelyMovingItemAtIndexPath(_ indexPath: NSIndexPath, withTargetPosition position: CGPoint) -> UICollectionViewLayoutAttributes
>
> Why would you prevent a subclass to compute an other indexPath or target
> position before calling super ?
>
>
>
>
>
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