[swift-evolution] final + lazy + fileprivate modifiers
Xiaodi Wu
xiaodi.wu at gmail.com
Fri Feb 17 13:11:14 CST 2017
On Fri, Feb 17, 2017 at 12:45 PM, Vladimir.S <svabox at gmail.com> wrote:
> On 17.02.2017 20:48, Xiaodi Wu wrote:
>
>> What you are really asking for is a way of flexibly designating a "unit of
>> code" within a module, for which the general solution is submodules. The
>> objection is that, instead of tackling that issue, these are suggestions
>> to
>> invent ad-hoc units of code (scope + extensions only in the same file,
>> scope + extensions only in the same module, class + extensions only in the
>> same file + subclasses only in the same module), and it is possible to
>> invent arbitrary many of these.
>>
>
> No, sorry, I don't agree with you.
> Current situation forces us to generate huge source files or write each
> type in its own submodule/file. IMO it is very naturally to have a need to
> protect access to some details *even* in the same file(please find David
> Sweeris's answer in previous email in this thread. with current 'private'
> he can *guarantee* that no code touches internal props even in the same
> file), also many of us need a way to share some details only for
> extensions/subtypes in other files in the same module/submodule even just
> to organize code as *one* need/want and to express intention about who
> should "touch" this code and get help from compiler when accidentally try
> to use protected method/prop.
>
I reject the premise that it is a goal of the Swift compiler to protect you
from yourself.
You can *guarantee* that nothing in the same file touches what it shouldn't
touch *by your own eyes*; `private` makes it "easier" but it is by no means
necessary. Indeed I argue that reading code should be the go-to way reason
about the behavior of code, and that compiler help is justified only when
such a method of reasoning is unusually hard or error-prone.
Likewise, you can express intention by documentation. Indeed I argue that
reading the documentation should be the go-to way for a reader to learn how
to use unfamiliar code. Since a user will consult the documentation if he
or she is wondering, "how or when should I use this method?", it is
perfectly sufficient and elegant to put a sentence in the documentation
that says, "actually, you should never use this method." It is self-evident
why one might _want_ compiler help, but it is unclear to me why one _needs_
compiler help for this: after all, if you call an internal method that
doesn't behave as intended, you can read the source code to find out
exactly why--you can even change it!
Someone, who want just internal/public can use only them in own code, no
> problems. But many feels that they need a more detailed access levels to
> structure their code, they find current situation not comfortable.
>
As I said, there are arbitrarily many ways to structure your code. If you
insist that the compiler should help you to control, perfectly, exactly
what lines of code can call what other lines of code, and that the way to
spell this desire is through access levels, then you will need many more
access levels. My point is that, taken to its logical end, you would need
infinitely many access levels. Although it would be unnecessary for the
language to active prohibit certain styles of organizing code, I believe
very strongly it is a non-goal of Swift to actively support, by the
addition of new features, all imaginable styles of organizing code.
>
>
>> There is, objectively, an actual minimum number of access modifiers, which
>> is two. Those two are: visible only inside the unit of code, or visible
>> both inside and outside the unit of code. In Swift, those are spelled
>> internal and public. Everything else here is really talking about better
>> or
>> more flexible ways of defining a unit of code.
>>
>>
>> On Fri, Feb 17, 2017 at 06:21 Vladimir.S via swift-evolution
>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>
>> On 17.02.2017 11:29, Slava Pestov via swift-evolution wrote:
>> >
>> >> On Feb 17, 2017, at 12:09 AM, Charlie Monroe via swift-evolution
>> >> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org
>> >>>
>>
>> wrote:
>> >>
>> >> True, what I meant was a wider feedback - let's face it, there are
>> many
>> >> more Swift developers now than 2 years ago.
>> >>
>> >> My objection is not to the documentation itself, but to the fact
>> that I'm
>> >> unnecessarily exposing an internal implementation detail to the
>> rest of
>> >> the module. Being able to hide it from the rest IMHO leads to
>> better
>> >> though-through API that is indeed meant to be exposed; whereas
>> exposing
>> >> internal details leads to allowing various quick hacks instead. We
>> know
>> >> these quick hacks very well from the ObjC world by accessing
>> private
>> >> parts of the object via duck typing or setting values via KVO.
>> >>
>> >> At least this is my experience with which the less implementation
>> details
>> >> are exposed to the outer world, the better.
>> >
>> > I think the fundamental disagreement we’re seeing in this thread is
>> the
>> > meaning of “outer world”; to some, it means “users of your module”.
>> To
>> > others, it also means “other developers on my team who are working
>> on
>> other
>> > files in the module”.
>> >
>> > Personally I feel enforced encapsulation of implementation detail
>> to the
>> > latter group is less important than the former, and can be handled
>> by
>> > convention. Whereas other users of your module definitely benefit
>> from
>> > access control and being able to consume a clearly-defined
>> interface.
>>
>> I assume we are discussing access modifiers mainly for the former
>> group,
>> i.e. when we are "inside" the module (even when this module is
>> written by
>> the same one person, and especially when it is written by the group).
>>
>> "handled by convention" - are we talking about something like
>> declaring
>> props and methods as __privateprop , m_privateprop etc and write
>> comments
>> to mark that they should not be used outside of some scope? Is it
>> really
>> Swifty and acceptable for the modern language? Will this help to
>> prevent
>> some mistakes with incorrect access? Is it better than simple and
>> clean
>> schema for access modifiers and compiler's help? I don't understand
>> this.
>>
>> IMO, access modifiers is very known and handy abstraction to distinct
>> levels of access and to structure code many developers knows about
>> and use
>> in other languages.
>> At the end, if one wants to keep all internal - no problems!, you can
>> do
>> this right now, just don't use fileprivate/private/etc.
>>
>> Yes, I agree we need a simple and clean schema, not over-complicated,
>> we
>> need nice&clean keywords, we need a required minimum of access
>> modifiers,
>> not more, and I do believe currently we don't have this minimum.
>>
>> Was already suggested, trying again(I do believe this could be a
>> compromised solution to suit needs of the main part of developers):
>> * (as currently) public/open -> outside of the module
>> * (as currently) internal -> inside module
>> * private -> inside file (instead of fileprivate)
>> * protected(or *other* keyword) -> inside file + subtype&extensions
>> in the
>> *same module*
>>
>> What objections could be made for this?
>> Thank you.
>>
>> >
>> > Slava
>> >
>> >>
>> >>> On Feb 17, 2017, at 8:54 AM, Xiaodi Wu <xiaodi.wu at gmail.com
>> <mailto:xiaodi.wu at gmail.com>
>> >>> <mailto:xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>>> wrote:
>> >>>
>> >>> That blog post starts out right away to say that it's a response
>> to
>> >>> community feedback. Moreover, the scenario you describe was just
>> as
>> >>> possible in 2014 as it is now. Finally, then as now, it's unclear
>> why
>> >>> you consider documentation to be "not pretty." After all, your
>> reader
>> >>> would need to consult the documentation before using a variable
>> anyway.
>> >>> On Fri, Feb 17, 2017 at 01:04 Charlie Monroe via swift-evolution
>> >>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org
>> >>>
>> wrote:
>> >>>
>> >>> I'm aware of this, but that's fairly a long time ago - before
>> Swift
>> >>> was open source and had community feedback and before Swift
>> was
>> used
>> >>> widely among developers.
>> >>>
>> >>> To me, real-world use of the language has shown some flaws of
>> >>> missing a protected access control, mainly having to decide
>> between
>> >>> having a variable internal or cramming all of the class
>> extension
>> >>> into one file, making it a 3KLOC mess. Either solution is not
>> pretty
>> >>> - now I have it split among several files with an internal
>> variable
>> >>> commented as "Do not use, for private use of this class only."
>> >>>
>> >>>> On Feb 17, 2017, at 7:47 AM, Jose Cheyo Jimenez
>> >>>> <cheyo at masters3d.com <mailto:cheyo at masters3d.com>
>> <mailto:cheyo at masters3d.com <mailto:cheyo at masters3d.com>>> wrote:
>> >>>>
>> >>>> https://developer.apple.com/swift/blog/?id=11
>> >>>>
>> >>>>
>> >>>>
>> >>>> On Feb 16, 2017, at 10:05 PM, Charlie Monroe via
>> swift-evolution
>> >>>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org
>> >
>> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org
>> >>>
>> wrote:
>> >>>>
>> >>>>> How about removing fileprivate, getting Swift 2 meaning of
>> private
>> >>>>> (as most people here now suggest) and add additional
>> @protected
>> >>>>> annotation for those who want a more fine-grained solution:
>> >>>>>
>> >>>>> @protected private - members accessable only from the
>> >>>>> class/struct/enum/... and their extensions within the file
>> >>>>>
>> >>>>> @protected internal - again, but you can access it even from
>> >>>>> extensions and subclasses outside of the file within the
>> entire
>> >>>>> module.
>> >>>>>
>> >>>>> @protected public/open - the same as above, but outside the
>> modules.
>> >>>>>
>> >>>>> To me, this way most people here will be happy:
>> >>>>>
>> >>>>> - those wishing the access control gets simplified - it in
>> fact
>> >>>>> does, you don't need to use @protected, if you don't want
>> to/need to.
>> >>>>> - those who need a fine-grained solution, here it is.
>> >>>>>
>> >>>>>
>> >>>>>
>> >>>>>> On Feb 17, 2017, at 3:49 AM, Matthew Johnson via
>> swift-evolution
>> >>>>>> <swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org>>> wrote:
>> >>>>>>
>> >>>>>>
>> >>>>>>
>> >>>>>> Sent from my iPad
>> >>>>>>
>> >>>>>>> On Feb 16, 2017, at 8:36 PM, David Sweeris via
>> swift-evolution
>> >>>>>>> <swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org>>>
>> >>>>>>> wrote:
>> >>>>>>>
>> >>>>>>>
>> >>>>>>>> On Feb 16, 2017, at 14:34, Slava Pestov via
>> swift-evolution
>> >>>>>>>> <swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org>>>
>> >>>>>>>> wrote:
>> >>>>>>>>
>> >>>>>>>> While we’re bikeshedding, I’m going to add my two cents.
>> Hold
>> >>>>>>>> on to your hat because this might be controversial here.
>> >>>>>>>>
>> >>>>>>>> I think both ‘private’ and ‘fileprivate’ are unnecessary
>> >>>>>>>> complications that only serve to clutter the language.
>> >>>>>>>>
>> >>>>>>>> It would make a lot more sense to just have internal and
>> public
>> >>>>>>>> only. No private, no fileprivate, no lineprivate, no
>> protected.
>> >>>>>>>> It’s all silly.
>> >>>>>>>
>> >>>>>>> Eh, I've used `private` to keep myself honest in terms of
>> going
>> >>>>>>> through some book-keeping functions instead of directly
>> >>>>>>> accessing a property.
>> >>>>>>
>> >>>>>> This is exactly the kind of thing I like it for and why I
>> hope we
>> >>>>>> might be able to keep scoped access even if it gets a new
>> name
>> >>>>>> that ends up as awkward as fileprivate (allowing private to
>> >>>>>> revert to the Swift 2 meaning).
>> >>>>>>
>> >>>>>>>
>> >>>>>>> - Dave Sweeris
>> >>>>>>> _______________________________________________
>> >>>>>>> swift-evolution mailing list
>> >>>>>>> swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org> <mailto:swift-evolution at swift.org
>> <mailto:swift-evolution at swift.org>>
>> >>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> >>>>>>
>> >>>>>> _______________________________________________
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