[swift-evolution] [Discussion] Enforcing Calling Super

[Matthew Johnson]

> 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.

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