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

Leonardo Pessoa me at lmpessoa.com
Thu Jul 7 13:05:16 CDT 2016


Goffredo, sorry if it felt offensive. It was not my intention. I've dealt with so many different libraries where, as many already pointed out here, has to rely on "fixing" the library themselves. This is not what a library was supposed to be and I might have left a few of my bad experiences speak louder.

L

-----Original Message-----
From: "Goffredo Marocchi" <panajev at gmail.com>
Sent: ‎07/‎07/‎2016 01:39 PM
To: "Leonardo Pessoa" <me at lmpessoa.com>
Cc: "Jean-Daniel Dupas" <mailing at xenonium.com>; "swift-evolution" <swift-evolution at swift.org>
Subject: Re: [swift-evolution] [Review] SE-0117: Default classes to benon-subclassable publicly

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. 


Seriously though


Mine is the opinion of a library-maker,
yours of the user of poorly designed/developed libraries.


this kind of attitude on this list got to stop.

Sent from my iPhone

On 7 Jul 2016, at 17:23, Leonardo Pessoa via swift-evolution <swift-evolution at swift.org> wrote:


Jean, IMO marking every class as subclassable means the creator does
not care for you to design and develop a great library because s/he is
not caring for the library at all. I right now have to go through the
burdensome activity of marking too many classes/methods as final to
prevent misuse of my libraries and find good design workarounds when I
need to subclass internally what I don't want you to subclass.

IMO the usage of a library is to be crafted/planned/designed by their
developers not their users. Mine is the opinion of a library-maker,
yours of the user of poorly designed/developed libraries. By pushing
this proposal, developer of such libraries will have much burden to
make/keep a poor library or will have to work on better
design/implementation for it to suit its purpose.

L

On 7 July 2016 at 13:08, Jean-Daniel Dupas via swift-evolution
<swift-evolution at swift.org> wrote:

* What is your evaluation of the proposal?



Strong -1 too.



I can’t count the number of times it save my hours tone able to override

arbitrary classes and methods.



Sometimes to simply add log point to understand how the API work. Other

times to workaround bugs in the library. Or even to extends the library in a

way that the author did not intent in the first place, but that was

perfectly supported anyway.



I already see how libraries author will react to that new default. They will

either don’t care and mark all classes as subclassable, or find to

burdensome to get subclassability right and prohibit subclassing all

classes.





Le 7 juil. 2016 à 02:27, Jonathan Hull via swift-evolution

<swift-evolution at swift.org> a écrit :



* What is your evaluation of the proposal?



A **strong** -1



First, I have often found that you can’t always predict the way which

something will need to be extended.  You think you know, but are then

surprised by creative uses.  My favorite features of Swift/Cocoa involve

retroactive modeling.



Second, I don’t think this proposal will achieve its stated objective of

forcing people to think about subclassing more.  It will just add confusing

boilerplate.



Things like Swift optionals work well because they make the (often

forgotten) choices explicit in the context that they are used.  In the world

of Human Factors, we call it a forcing function.  This proposal has the

inverse structure, and will be ineffective, because the “forcing” part of it

shows up in a different context (i.e. trying to use a framework) than the

decision is being made in (writing the framework).  This type of thinking

leads to things like Java and the DMV.



As Tino said:



No matter what the defaults are, good libraries are hard to build, so I

predict this proposal would not only fail in increasing framework quality,

but also will make it much harder for users of those frameworks to work

around their flaws, which are just a natural part of every software.



I think he is right on here.  Those who were prone to be thoughtful about

their design would have been anyway.  Those who are not thoughtful about

their design will just leave these annotations off… leaving us with no

recourse to extend/modify classes.  When people complain, they will add the

annotations without actually thinking about the meaning (i.e. stack overflow

/ the fixit tells me I need to add this word to make the compiler happy).

All this does is put framework users at the mercy of the framework writers.





Finally, this proposal is missing important aspects of the problem space.

If we truly want to solve the issue of subclassing, we need to consider all

of the common issues which arise.  Looking at the cocoa documentation you

will see several types of annotations:

1) This method MUST be overridden

2) This method should NOT be overridden

3) This method MUST be called

3) This method should NOT be called except by subclasses

4) This method should NOT be called except by a method override calling

super

5) This method MUST call super

6) Overrides of this method should NOT call super



If we are attempting to bring thoughtfulness to the design of classes, I

would like to see things be extendable by default, but with annotations that

thoughtful framework designers can use to designate how a particular method

should be used.  In most cases, it should not explicitly forbid the end user

from subclassing, but require them to acknowledge that what they are doing

is not intended by the framework. (e.g. "unsafe override func"…).  That

would feel 1000x more swifty to me.  Opt-out safety.



* Is the problem being addressed significant enough to warrant a change to

Swift?



No. It doesn’t actually solve the problem... and I haven’t actually run into

this problem in the real world.



* Does this proposal fit well with the feel and direction of Swift?



No, it gives Swift more of a feeling of busywork and unnecessary boilerplate

while failing to achieve its objective.  It goes against the retroactive

modeling allowed by other areas of Swift.



* If you have used other languages or libraries with a similar feature, how

do you feel that this proposal compares to those?



I tend to avoid languages which require this sort of thing.  In other

languages that lock things down, there is a need to unlock things soon after

(e.g. friend classes).



I predict the same thing will happen here.  People will quickly be asking

for the ability to patch/override in cases where the framework designer was

wrong.  That shows a problem inherent with the design...



* How much effort did you put into your review? A glance, a quick reading,

or an in-depth study?



Read the proposal & discussion.  Read earlier discussions around access

control that touched on this subject as well.  I have been designing

frameworks for years.



Thanks,

Jon



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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