[swift-evolution] [swift-evolution-announce] [Review] SE-0159: Fix Private Access Levels

Jose Cheyo Jimenez cheyo at masters3d.com
Tue Mar 21 16:26:42 CDT 2017 

> On Mar 21, 2017, at 11:54 AM, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On Mar 21, 2017, at 1:41 PM, David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>> 
>> 
>> 
>> Sent from my iPhone
>> On 21 Mar 2017, at 16:57, Drew Crawford <drew at sealedabstract.com <mailto:drew at sealedabstract.com>> wrote:
>> 
>>> 
>>> 
>>>> > I’m not arguing that it is less or more than a majority. I’m just saying that we’ve seen a lot of talk against the original change.
>>> 
>>> This proposal asks us to balance the convenience of one group (extension-writers) against the existence of another (scoped-access users).  To do that, we need a clear idea of the composition of both groups.
>>> 
>>> “A lot of talk” is not the evidentiary standard to remove a feature.  It was not good enough when we introduced the feature, that required argument and clear use-cases.
>>> 
>> "A lot of talk" is not the evidence supporting the proposal: it's just a warning that something may be very controversial among the community. The arguments for the revert are in the proposal and in the discussions in this thread.
>> 
>>>> > By default, I did not mean the syntactic default of the language but the access modifier users will use “by default” when trying to restrict visibility. In most languages, that keyword is “private” so its valid to say that newcomers to the language will “default” to using that one.
>>> 
>>> Apologies, but I do not understand the argument:
>>> 
>>> A user wants to restrict visibility (e.g. they are dissatisfied with “internal”)
>>> The user *chooses* private because of familiarity from another language
>>> The user is then surprised that their choice of private indeed restricted the visibility, thus achieving their goal?
>>> What language does the user come from in which “private” is file-visible?  It isn’t Java, C++, or PHP.  C#’s “partial” is the closest I can think of, and it isn’t at all close.
>> 
>> It has pointed quite a few times by core team members that comparison to languages is not a very strong arguments, especially when Swift does things differently for a good reason. I can't stop from quoting Xiaodi from a month back:
>> 
>> «The beauty of Swift 2's access modifiers was that they were based around files and modules, explicitly rejecting types and scopes as units for determining visibility.» -- Xiaodi
>> 
>>> A user who wants a middle-ground visibility would “default” to “protected”, “friend”, “partial”, or similar.  After that does not compile, they will use google to find a middle-road visibility keyword, for which the only candidate is “fileprivate”.  But they will not choose “private”, it’s just not a reasonable expectation of what the keyword means to a new Swift developer.
>>> 
>>> The popularity of private “as a default” is simply because many users prefer to hide their implementation details as a matter of routine code hygiene.  Redefining private in order to thwart their code hygiene goal seems extreme.
>> 
>> The point is that keeping both private and fileprivate feels like an un-necessary complication:
>> 
>> • either a programmer falls on your side of the fence and will use private as often as possible and relegate to fileprivate when the design leaves no other choice. At that point it feels like a language wart.
>> • or a programmer will fall on my side of the fence and use fileprivate all the time and the language feels like it has an unnecessary access modifier.
>> 
>> I'd argue that the cases when a programmer will use both meaningfully is very rare. As a consequence, we should try to only keep one. Removing fileprivate is a no-go with extensions so that leaves us with removing private.
> 
> Removing scoped access is a no-go if we consider tightly encapsulating invariant-preserving state to be an important feature.  The fact is that both features can be used meaningfully.  The fact that some people choose not to do this is not an argument against the features being available.  It is an opportunity to encourage people to thing more carefully about why they are encapsulating something.  

I understand the bigger picture you are getting at but the scope access you have envisioned should not be called private. 

In order to get scope access to a place where it is more useful we have to remove it.

I don’t mind if scope access is kept but it must have a different name and that should be a different limited scope proposal. 

Opposing SE-0159 will make it much harder to redefine scope access.


> 
> A programmer has to make a conscious decision to give a declaration visibility other than internal.  If they have trouble identifying whether file or scoped access is appropriate this indicates they don’t really understand their intent in encapsulating the declaration very clearly.  I don’t think it’s a bad thing to ask people to think about this a little bit more.  A simple guideline is to use file-level access unless you have a specific reason for preferring the tight encapsulation scoped access provides.  Both Drew and I have offered some examples of specific reasons for using scoped access that IMO are important enough that they deserve to be supported by the language.
> 
>> 
>>> I agree with several here (as I did in SE-0025) that our access modifiers are not well-named.  However, that’s not the proposal in front of us.
>>> 
>>>> > My own statistics in my projects show the contrary. At best, this shows how divisive this feature is.
>>> 
>>> This *may* show that, if contrary statistics were presented, but that hasn’t occurred.
>>> 
>> I can generate statistics from my projects if you want. But it's unnecessary: I haven't used private once since it's introduction in Swift 3. I don't see the advantages it brings worth the trouble.
>>>> In old code, statistics could be biased by the migrator having replaced all previous instances of private by fileprivate.
>>> 
>>> If the migrator migrated code to private, and it *worked* (e.g. did not introduce visibility errors) this is not bias, this is a correct use of the feature.
>>> 
>> The migrator migrated to fileprivate everywhere, not private, disagreeing with your use of fileprivate.
>> 
>>>> > I'm just arguing that the additional scope-based access modifier does not provide enough differentiation to be worth that complexity.
>>> 
>>> The only argument I have seen so far around “complexity” boils down to: “some people do not use it”.  But some people *do* use it, and anyway if we are going to remove all the features “not enough people” use then we are in for a ride.
>>> 
>> Some people used the for(;;) loop, the ++ operator, var parameters. Many other features were removed from Swift to simplify he language, make it more consistent. Those are worthwhile goals. Yes, we are past Swift 3 now, but that doesn't mean we shouldn't be able to propose a few rare breaking proposals. The implementation of access modifiers came so late in the Swift 3 timeframe that we had little time to play around with them before Swift 3 was released. Now that we have, we have a short window of time to fix mistakes that were made. I'm just arguing that the proposal was one of those mistakes. But you have a right to disagree.
>>> Swift 3 shipped, so what we are discussing now is yanking a keyword without replacement.  There is code written that uses private to enforce its threading or security invariants.  There is code written that uses private in order to shadow another declaration.   There is code that will not compile after migration. We need more than a vague fear of complexity generally to throw a brick through all those windows.  That brick will introduce quite a bit of complexity itself.
>>> 
>>>> Concerning the one-class-per-file argument, I would suggest this counter-argument: when working in large projects, I believe it's a good thing if the language encourages (forces is too strong a word for my taste) a one class per file structure, it's good practice.
>>> 
>>> The form of the argument is invalid.  Suppose I argued: "it’s a good thing for the language to encourage one definition per class (no extensions), it’s good practice.  So we do not need fileprivate.”  That would be very silly (although it has already been advanced as a straw-man position elsewhere in this thread). The argument that we do not need private because nobody should put multiple classes in a file is equally silly. There are reasons to do so, in fact one motivation was given in SE-0025:
>>> 
>>>> > Putting related APIs and/or related implementations in the same file helps ensure consistency and reduces the time to find a particular API or implementation. 
>>> 
>>> 
>>> These concerns are not resolved by arguments of the form “just don’t do that”.
>>> 
>>> I empathize with the Swift2 programmer who got through two releases without a scoped access modifier and is annoyed by change.  However, removing the feature now is more change, not less, so it makes their problem worse, not better.
>>> 
>>> 
>>> On March 21, 2017 at 2:17:40 AM, David Hart (david at hartbit.com <mailto:david at hartbit.com>) wrote:
>>> 
>>>> Perhaps it was a mistake, but I purposefully did not go into too much detail in the proposal because I think this debate is purely a question of philosophy on Swift and its language features. I did not want to add un-necessary bloat that would have added little rationalisation. Let me try to explain the holes in the proposal by answering your review:
>>>> 
>>>>> On 21 Mar 2017, at 02:26, Drew Crawford via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> I disagree quite strongly with the proposal.
>>>>> 
>>>>> First, the document draws conclusions without apparent supporting evidence, e.g.
>>>>> 
>>>>> > Since the release of Swift 3, the access level change of SE–0025 was met with dissatisfaction by a substantial proportion of the general Swift community. Those changes can be viewed as actively harmful, the new requirement for syntax/API changes.
>>>>> What is “dissatisfaction by a substantial proportion of the general Swift community”? How was this measured/determined?
>>>> It’s not feasible to measure precisely the feeling of a whole community. But we get a feeling for it by following the mailing-list, by talking to colleagues, by reading twitter, etc… And it think we all agree that the debate is highly divisive and that a “substantial proportion” of the community was dissatisfied: I’m not arguing that it is less or more than a majority. I’m just saying that we’ve seen a lot of talk against the original change.
>>>>> What was done to control for the population happy with SE-0025 who would e.g. not be likely to take up pitchforks?
>>>> That’s why its important we have this debate now.
>>>>> Who argues these changes are “actively harmful” and where were they during SE-0025?
>>>> The proposal makes the argument that the changes are actively harmful. It’s now up to debate. By the way, even if several people (including me) were already against this proposal during the review, I don’t see why anybody would not have the right to change his mind, especially after several months of production usage and argue differently now.
>>>>> > subtly encourages overuse of scoped access control and discourages the more reasonable default
>>>>> Who claims that scoped access is “overused” and what is their argument for doing so?
>>>>> Why is “fileprivate” the “more reasonable default”? In fact neither fileprivate *nor* private are default (reasonable or not!). Internal is the default. Nor does this proposal suggest we change that. So this seems a very strange statement.
>>>> By default, I did not mean the syntactic default of the language but the access modifier users will use “by default” when trying to restrict visibility. In most languages, that keyword is “private” so its valid to say that newcomers to the language will “default” to using that one. If the proposal is accepted, file-scoped private will regain that status.
>>>>> > But is that distinction between private and fileprivate actively used by the larger community of Swift developers?
>>>>> Yes. To cite some evidence, here are codebases I actively maintain:
>>>>> 
>>>>> | codebase                                               | private # | fileprivate # | ratio |
>>>>> 
>>>>> |--------------------------------------------------------|-----------|---------------|-------|
>>>>> 
>>>>> | "M" (proprietary)                                      | 486       | 249           | 2x    |
>>>>> 
>>>>> | "N"(proprietary)                                       | 179       | 59            | 3x    |
>>>>> 
>>>>> | NaOH https://code.sealedabstract.com/drewcrawford/NaOH <https://code.sealedabstract.com/drewcrawford/NaOH> | 15        | 1             | 15x   |
>>>>> 
>>>>> | atbuild https://github.com/AnarchyTools/atbuild <https://github.com/AnarchyTools/atbuild>        | 54        | 5             | 11x   |
>>>>> 
>>>>> So from my chair, not only is the distinction useful, but scoped access control (private) is overwhelmingly (2-15x) more useful than fileprivate.
>>>>> 
>>>> My own statistics in my projects show the contrary. At best, this shows how divisive this feature is. During the discussion of this proposal, it was argued that making decisions based upon project statistics would be dangerous:
>>>> 
>>>> In old code, statistics could be biased by the migrator having replaced all previous instances of private by fileprivate.
>>>> In new code, satistics could be biased by people using private because of it being the “soft-default”, regardless of proper semantics.
>>>>> > And if it were used pervasively, would it be worth the cognitive load and complexity of keeping two very similar access levels in the language? This proposal argues that answer to both questions is no
>>>>> 
>>>>> This proposal does not make any later argument about “cognitive load” or “complexity” I can identify.  Did the proposal get truncated?
>>>>> 
>>>> Sorry if I did not state it explicitly, but I see any feature/keyword added to the language as “additional complexity”. And that complexity is completely worth it when the feature adds significant expressivity. I'm just arguing that the additional scope-based access modifier does not provide enough differentiation to be worth that complexity.
>>>>> What is stated (without evidence) is that "it is extremely common to use several extensions within a file” and that use of “private” is annoying in that case.  I now extend the above table
>>>>> 
>>>>> | codebase                                               | private # | fileprivate # | ratio | # of extensions (>=3 extensions in file) |
>>>>> 
>>>>> |--------------------------------------------------------|-----------|---------------|-------|------------------------------------------|
>>>>> 
>>>>> | "M" (proprietary)                                      | 486       | 249           | 2x    | 48                                       |
>>>>> 
>>>>> | "N"(proprietary)                                       | 179       | 59            | 3x    | 84                                       |
>>>>> 
>>>>> | NaOH https://code.sealedabstract.com/drewcrawford/NaOH <https://code.sealedabstract.com/drewcrawford/NaOH> | 15        | 1             | 15x   | 3                                        |
>>>>> 
>>>>> | atbuild https://github.com/AnarchyTools/atbuild <https://github.com/AnarchyTools/atbuild>        | 54        | 5             | 11x   | 6                                        |
>>>>> 
>>>>> in order to demonstrate in my corner of Swift this is not “extremely common”, and is actually less popular than language features the proposal alleges aren’t used.
>>>>> 
>>>>> My point here is that **different people in different corners of the community program Swift differently and use different styles**.  I can definitely empathize with folks like the author who use extensions to group functions and are annoyed that their favorite visibility modifier grew four extra characters.  Perhaps we can come up with a keyword that is more succint.
>>>>> 
>>>> I agree that different people in different corners use different styles. But you could use that argument to validate many features which would make a group of users happy; but all those feature together would just add bloat to the language. Swift has been known to be a very opinionated language, to keep the language simple yet expressive.
>>>>> However, that is no reason to take away features from working codebases.  A scoped access modifier is perhaps my favorite feature in Swift 3.  Let’s not throw stuff away because it adds extra characters to one programming style.
>>>>> 
>>>>> Finally, SE-0025 establishes clear motivation for the scoped access modifier:
>>>>> 
>>>>> > Currently, the only reliable way to hide implementation details of a class is to put the code in a separate file and mark it as private. This is not ideal for the following reasons:
>>>>> 
>>>>> > It is not clear whether the implementation details are meant to be completely hidden or can be shared with some related code without the danger of misusing the APIs marked as private. If a file already has multiple classes, it is not clear if a particular API is meant to be hidden completely or can be shared with the other classes.
>>>>> 
>>>>> > It forces a one class per file structure, which is very limiting. Putting related APIs and/or related implementations in the same file helps ensure consistency and reduces the time to find a particular API or implementation. This does not mean that the classes in the same file need to share otherwise hidden APIs, but there is no way to express such sharability with the current access levels.
>>>>> 
>>>>> As far as I can see, the proposal does not actually address or acknowledge these problems at all, but cheerfully returns us to them.  It would be a mistake to deprecate this feature without examining at all why we introduced it.  And realistically we need new solutions to those problems before removing the existing one.
>>>>> 
>>>>> Drew
>>>>> 
>>>>> On March 20, 2017 at 6:54:55 PM, Douglas Gregor (dgregor at apple.com <mailto:dgregor at apple.com>) wrote:
>>>>> 
>>>>> Hello Swift community,
>>>>> 
>>>>> The review of SE–0159 “Fix Private Access Levels” begins now and runs through March 27, 2017. The proposal is available here:
>>>>> 
>>>>> https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md <https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.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 <https://lists.swift.org/mailman/listinfo/swift-evolution> or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:
>>>>> 
>>>>> Proposal link:
>>>>> 
>>>>> https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md <https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md> Reply text Other replies What goes into a review?
>>>>> 
>>>>> The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine 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 <https://github.com/apple/swift-evolution/blob/master/process.md> Thank you,
>>>>> 
>>>>> -Doug
>>>>> 
>>>>> Review Manager
>>>>> 
>>>>> swift-evolution-announce mailing list swift-evolution-announce at swift.org <mailto:swift-evolution-announce at swift.org> https://lists.swift.org/mailman/listinfo/swift-evolution-announce <https://lists.swift.org/mailman/listinfo/swift-evolution-announce>_______________________________________________
>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>>> 
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170321/66ca601a/attachment.html>

More information about the swift-evolution mailing list