[swift-evolution] [Review #2] SE-0117: Default classes to be non-subclassable publicly

[Jean-Daniel Dupas]

> Le 16 juil. 2016 à 18:05, Jose Cheyo Jimenez via swift-evolution <swift-evolution at swift.org> a écrit :
> 
>> 	* What is your evaluation of the proposal?
> 
> +1 as before but I do have concerns
> 
> 	* Why do open classes need to have also have open superclasses? 
> 	* I don’t think sealed methods/properties as default is the right default. 
> 	* If the default was open for methods/properties, then do we really need the sealed keyword? Could’t we just use final for that?
> 
>> 	* Is the problem being addressed significant enough to warrant a change to Swift?
> 
> Yes
> 
>> 	* Does this proposal fit well with the feel and direction of Swift?
> 
> Requiring super classes to also be Open seems wrong. 

> 
> I agree with Kevin Ballard on being open by default for methods/ properties http://article.gmane.org/gmane.comp.lang.swift.evolution/23467/ <http://article.gmane.org/gmane.comp.lang.swift.evolution/23467/>
> 
> If we are open by default for methods/properties then we could simplify things by just using final for methods that need to be sealed; I don’t see the need to have sealed methods/properties outside of the module ONLY. 
> 
> We already have to mark all public methods/properties as public, if I need something not the be overridable then I can just use final. This would work the same across all classes. 
> 
> If I was a framework author that initially just had a library that was sealed but then somebody asked me to make it open; All I would want to do is add open to the class only, I would not want to spend the time to go back an add open to all public methods/properties specially if I am already using final. I think having method/properties open by default is the best compromised. I can see framework authors switching a class to be open and expecting that everything in the class in open and if they don’t open any methods, then what possible use is a subclass than an extension could not provide?

Extensions do not support stored properties (yet?). Subclasses do. That said, I agree that having an open class without any open member does not has much benefit, but I’m sure we can find a valid use case for such class.

> I think that is an overreach to make the framework author have to add open to every public method in addition to having to open every super class. As a framework author if I think my clients could use subclassing, all I want to do is flip a switch on the classes that I want to make subclass able  and then just push a new version. As a framework user I want to be able to tell my framework author “can you just add open to classes abs and deca etc.” I think it is more likely that I will get my request if it is easy vs it the framework author needs to touch every class in the hierarchy. 
> 
> 
>> 	* If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> n/a
>> 	* How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> 
> reviewed previously and followed the update. 
> 
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