<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br><br>Sent from my iPad</div><div><br>On Jul 7, 2016, at 5:15 PM, John McCall via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8">n Jul 7, 2016, at 9:39 AM, Goffredo Marocchi via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><div><blockquote type="cite" class="">I disagree that a stable for over 30 years of every OOP language that I know is equivalent to lack of care for good library design, but if we want to push value types by making working with classes harder so be it :P. <br class=""></blockquote><div><br class=""></div>Making classes harder to work with is not a specific goal, no. :)</div><div><br class=""></div><div>I don't expect that this will be a significant burden for most Swift programmers. Mainly, that's because this only affects classes that are exposed outside of a module, and the great majority of non-system classes in a typical Cocoa program are single-purpose leaf classes that — at most — expose a few methods to other subsystems. Swift doesn't really encourage you write complex classes that are primarily customized with subclassing; it encourages the heavy use of value types, and it encourages customization through protocols and functions. In fact, that's not really new to Swift, it's a general lesson from the last few decades of software development: composing smaller, independent systems through well-defined interfaces leads to better software than building monolithic systems whose behavior can only be defined in reference to the whole.</div><div><br class=""></div><div>I sympathize with the argument about wanting to fix bugs and add features via override, but that's never been maintainable in the long term; you always just end up with superclasses that everyone is terrified to touch because every subclass has its own invasive "fixes", and that's even when working within a single codebase. With libraries, you can pretty quickly get locked in to a specific version because your customizations don't work with new releases; either that, or the maintainer just decides that they can't fix of their mistakes and so goes off to rewrite it from scratch. Either way, it's not good for the ecosystem.</div><div><br class=""></div><div>Plus, as others have mentioned, Swift already provides a lot of features that don't allow overriding: structs, final, etc. You simply cannot rely on overriding to fix upstream bugs the way that you can in most traditional OO languages because not enough code flows through calls to overridable methods. We should not compromise the goal of promoting stronger and more maintainable library designs just to maintain this illusion.</div><div><br class=""></div></div></blockquote><div><br></div><div>Thanks for continuing to make the case for this John. I really, really hope the core team will accept the proposal (with revisions - the problems with the keyword names are real). </div><div><br></div><div>It will clearly ruffle a lot of feathers but is worth doing in this case IMO. Especially since many commenters who are opposed do not seem to grasp a couple of crucial points:</div><div><br></div><div>1. As you point out, the majority of the surface area of idiomatic Swift APIs are unlikely to be impacted (value types, protocols, and final classes). This is very likely to apply to future Swift-native APIs from Apple regardless of the outcome of this proposal.</div><div><br></div><div>2. There is no impact on users of Apple's Objective-C APIs (AFAICT).</div><div><br></div><div>In the context of these facts, this proposal is not nearly as dramatic a change as many seem to be suggesting. It just tightens up an inconsistency in the language (the one area where public API contracts are not explicitly opted-in to).</div><div><br></div><div>-Matthew</div><br><blockquote type="cite"><div><div>John.</div><div><br class=""></div><div><blockquote type="cite" class=""><div class=""><div dir="auto" class=""><div class=""><br class=""></div><div class="">Seriously though</div><div class=""><br class=""></div><div class=""><blockquote type="cite" class=""><font class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">Mine is the opinion of a library-maker,<br class="">yours of the user of poorly designed/developed libraries.</span></font></blockquote><div class=""><br class=""></div>this kind of attitude on this list got to stop.<br class=""><br class="">Sent from my iPhone</div><div class=""><br class="">On 7 Jul 2016, at 17:23, Leonardo Pessoa via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><span class="">Jean, IMO marking every class as subclassable means the creator does</span><br class=""><span class="">not care for you to design and develop a great library because s/he is</span><br class=""><span class="">not caring for the library at all. I right now have to go through the</span><br class=""><span class="">burdensome activity of marking too many classes/methods as final to</span><br class=""><span class="">prevent misuse of my libraries and find good design workarounds when I</span><br class=""><span class="">need to subclass internally what I don't want you to subclass.</span><br class=""><span class=""></span><br class=""><span class="">IMO the usage of a library is to be crafted/planned/designed by their</span><br class=""><span class="">developers not their users. Mine is the opinion of a library-maker,</span><br class=""><span class="">yours of the user of poorly designed/developed libraries. By pushing</span><br class=""><span class="">this proposal, developer of such libraries will have much burden to</span><br class=""><span class="">make/keep a poor library or will have to work on better</span><br class=""><span class="">design/implementation for it to suit its purpose.</span><br class=""><span class=""></span><br class=""><span class="">L</span><br class=""><span class=""></span><br class=""><span class="">On 7 July 2016 at 13:08, Jean-Daniel Dupas via swift-evolution</span><br class=""><span class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</span><br class=""><blockquote type="cite" class=""><span class=""> * What is your evaluation of the proposal?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Strong -1 too.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">I can’t count the number of times it save my hours tone able to override</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">arbitrary classes and methods.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Sometimes to simply add log point to understand how the API work. Other</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">times to workaround bugs in the library. Or even to extends the library in a</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">way that the author did not intent in the first place, but that was</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">perfectly supported anyway.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">I already see how libraries author will react to that new default. They will</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">either don’t care and mark all classes as subclassable, or find to</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">burdensome to get subclassability right and prohibit subclassing all</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">classes.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Le 7 juil. 2016 à 02:27, Jonathan Hull via swift-evolution</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""><<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">* What is your evaluation of the proposal?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">A **strong** -1</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">First, I have often found that you can’t always predict the way which</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">something will need to be extended. You think you know, but are then</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">surprised by creative uses. My favorite features of Swift/Cocoa involve</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">retroactive modeling.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Second, I don’t think this proposal will achieve its stated objective of</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">forcing people to think about subclassing more. It will just add confusing</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">boilerplate.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Things like Swift optionals work well because they make the (often</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">forgotten) choices explicit in the context that they are used. In the world</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">of Human Factors, we call it a forcing function. This proposal has the</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">inverse structure, and will be ineffective, because the “forcing” part of it</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">shows up in a different context (i.e. trying to use a framework) than the</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">decision is being made in (writing the framework). This type of thinking</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">leads to things like Java and the DMV.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">As Tino said:</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">No matter what the defaults are, good libraries are hard to build, so I</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">predict this proposal would not only fail in increasing framework quality,</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">but also will make it much harder for users of those frameworks to work</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">around their flaws, which are just a natural part of every software.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">I think he is right on here. Those who were prone to be thoughtful about</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">their design would have been anyway. Those who are not thoughtful about</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">their design will just leave these annotations off… leaving us with no</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">recourse to extend/modify classes. When people complain, they will add the</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">annotations without actually thinking about the meaning (i.e. stack overflow</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">/ the fixit tells me I need to add this word to make the compiler happy).</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">All this does is put framework users at the mercy of the framework writers.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Finally, this proposal is missing important aspects of the problem space.</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">If we truly want to solve the issue of subclassing, we need to consider all</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">of the common issues which arise. Looking at the cocoa documentation you</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">will see several types of annotations:</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">1) This method MUST be overridden</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">2) This method should NOT be overridden</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">3) This method MUST be called</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">3) This method should NOT be called except by subclasses</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">4) This method should NOT be called except by a method override calling</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">super</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">5) This method MUST call super</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">6) Overrides of this method should NOT call super</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">If we are attempting to bring thoughtfulness to the design of classes, I</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">would like to see things be extendable by default, but with annotations that</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">thoughtful framework designers can use to designate how a particular method</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">should be used. In most cases, it should not explicitly forbid the end user</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">from subclassing, but require them to acknowledge that what they are doing</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">is not intended by the framework. (e.g. "unsafe override func"…). That</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">would feel 1000x more swifty to me. Opt-out safety.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">* Is the problem being addressed significant enough to warrant a change to</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Swift?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">No. It doesn’t actually solve the problem... and I haven’t actually run into</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">this problem in the real world.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">* Does this proposal fit well with the feel and direction of Swift?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">No, it gives Swift more of a feeling of busywork and unnecessary boilerplate</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">while failing to achieve its objective. It goes against the retroactive</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">modeling allowed by other areas of Swift.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">* If you have used other languages or libraries with a similar feature, how</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">do you feel that this proposal compares to those?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">I tend to avoid languages which require this sort of thing. In other</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">languages that lock things down, there is a need to unlock things soon after</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">(e.g. friend classes).</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">I predict the same thing will happen here. People will quickly be asking</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">for the ability to patch/override in cases where the framework designer was</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">wrong. That shows a problem inherent with the design...</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">* How much effort did you put into your review? A glance, a quick reading,</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">or an in-depth study?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Read the proposal & discussion. Read earlier discussions around access</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">control that touched on this subject as well. I have been designing</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">frameworks for years.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Thanks,</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Jon</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Hello Swift community,</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">The review of "SE-0117: Default classes to be non-subclassable publicly"</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">begins now and runs through July 11. The proposal is available here:</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0117-non-public-subclassable-by-default.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0117-non-public-subclassable-by-default.md</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Reviews are an important part of the Swift evolution process. All reviews</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">should be sent to the swift-evolution mailing list at</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">or, if you would like to keep your feedback private, directly to the review</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">manager.</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">What goes into a review?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">The goal of the review process is to improve the proposal under review</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">through constructive criticism and contribute to the direction of Swift.</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">When writing your review, here are some questions you might want to answer</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">in your review:</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> * What is your evaluation of the proposal?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> * Is the problem being addressed significant enough to warrant a change to</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Swift?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> * Does this proposal fit well with the feel and direction of Swift?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> * If you have used other languages or libraries with a similar feature, how</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">do you feel that this proposal compares to those?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> * How much effort did you put into your review? A glance, a quick reading,</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">or an in-depth study?</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">More information about the Swift evolution process is available at</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""> <a href="https://github.com/apple/swift-evolution/blob/master/process.md" class="">https://github.com/apple/swift-evolution/blob/master/process.md</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Thank you,</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">-Chris Lattner</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">Review Manager</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">_______________________________________________</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">swift-evolution mailing list</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><blockquote type="cite" class=""><span class="">_______________________________________________</span><br class=""></blockquote><blockquote type="cite" class=""><span class="">swift-evolution mailing list</span><br class=""></blockquote><blockquote type="cite" class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></blockquote><blockquote type="cite" class=""><span class=""></span><br class=""></blockquote><span class="">_______________________________________________</span><br class=""><span class="">swift-evolution mailing list</span><br class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></div></blockquote></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>swift-evolution mailing list</span><br><span><a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a></span><br><span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br></div></blockquote></body></html>