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

[Thorsten Seitz]

> Am 06.07.2016 um 13:39 schrieb Matthew Johnson via swift-evolution <swift-evolution at swift.org>:
> 
> 
> 
> Sent from my iPad
> 
>> On Jul 6, 2016, at 12:24 AM, Charlie Monroe via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Huge +1.
>> 
>> Question about inheritance though:
>> 
>> class A {} // Not publicly subclassable 
>> subclassable class B: A {} // Publicly subclassable
>> class C: B {} // Not publicly subclassable? Or is the subclassability inherited?
> 
> This is a great question.  There are really two questions: 
> 
> Can B be marked "subclassable" even though its superclass isn't?  Allowing this allows creation of new classes with A as an ancestor.  Since this is explicitly opt-in all within the same module I'm inclined to say we should allow it.  
> 
> Is subclassability inherited by in-module subclasses?  This seems to me opposed to the spirit of closed by default.  I think it is better to require annotation on *every* class an method that is open to extension outside the module, regardless of what choice a superclass makes,
> 
> This gives module authors the most control over *exactly* which classes can be used as superclasses outside the module (A and C don't need to be subclassable just because B needs to be.

I totally agree with both points.

-Thorsten 


> 
> -Matthew
> 
>> 
>> I'm not a big fan of the subclassable keyword either since it's quite long, not to mention it contains "class" which is the next keyword, making it visually repetitive.
>> 
>> I'd prefer open on both class and func to introduce only one keyword instead of two and possibly make it as a modifier of public to keep it in line with private(set)...
>> 
>>> On Jul 6, 2016, at 1:11 AM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Hello Swift community,
>>> 
>>> The review of "SE-0117: Default classes to be non-subclassable publicly" begins now and runs through July 11. The proposal is available here:
>>> 
>>>   https://github.com/apple/swift-evolution/blob/master/proposals/0117-non-public-subclassable-by-default.md
>>> 
>>> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at
>>> 
>>>   https://lists.swift.org/mailman/listinfo/swift-evolution
>>> 
>>> or, if you would like to keep your feedback private, directly to the review manager.
>>> 
>>> What goes into a review?
>>> 
>>> The goal of the review process is to improve the proposal under review through constructive criticism and contribute to the direction of Swift. When writing your review, here are some questions you might want to answer in your review:
>>> 
>>>   * What is your evaluation of the proposal?
>>>   * Is the problem being addressed significant enough to warrant a change to Swift?
>>>   * Does this proposal fit well with the feel and direction of Swift?
>>>   * If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
>>>   * How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
>>> 
>>> More information about the Swift evolution process is available at
>>> 
>>>   https://github.com/apple/swift-evolution/blob/master/process.md
>>> 
>>> Thank you,
>>> 
>>> -Chris Lattner
>>> Review Manager
>>> 
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