[swift-evolution] private & fileprivate

Zach Waldowski zach at waldowski.me
Fri Oct 7 16:05:09 CDT 2016

I third this sentiment. fileprivate is a nice idea and very clearly has
its uses (which is why the proposal got traction in the first place),
but when  combined with the other access levels, the language feature as
a whole feels arbitrary. In practical use, files that I felt were nicely
encapsulated and hiding implementation details are now a scattered mix
of access levels, adding cognitive load and making the code look
unorganized for having the gall to use extensions to split up

  Zachary Waldowski
  zach at waldowski.me

On Fri, Oct 7, 2016, at 01:55 PM, Russ Bishop via swift-evolution wrote:
>> On Oct 7, 2016, at 9:13 AM, David Hart via swift-evolution <swift-
>> evolution at swift.org> wrote:
>> I started the topic, but I also believe like you that the
>> *fileprivate* vs *private(file)* discussion has already been
>> thoroughly discussed and nothing new has been brought up. That’s not
>> what I want to discuss.
>> I instead want to share my experience using *private* and
>> *fileprivate* since release. Here are my thoughts:
>>  1. We should start with the premise that the proposal has added a
>>     substantial amount of complexity:
>>    1. It has added an extra modifier and access level to learn.
>>    2. It has complicated the access level rules with Inner types as
>>       mentioned in the *Complications with private types* section of
>>       the proposal.
>>    3. I have seen many people (twitter, work, slack) be confused
>>       about the difference between *private* and *fileprivate* at the
>>       global level. The answer is none, which shows that both
>>       modifiers are not very orthogonal.
>>    4. Since release, I saw people prefer one over the other, as a
>>       matter of style. They tend to always use *fileprivate* or
>>       always using *private*. In the latter case, functions and
>>       properties get clumped in the same class scope instead of be
>>       written through multiple extensions.
>>  2. I have the impression that the motivations for the proposal are
>>     much less real in practice:
>>    1. The first motivation stated is: *"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.”* I’ve found that to be fairly rare
>>       in practice because the implementation details only used to
>>       leak inside the same file, which greatly reduces the dangers.
>>    2. The second motivation stated is: *"It forces a one class per
>>       file structure, which is very limiting." *First of all, this is
>>       partly false. I think it forces putting classes which share
>>       implementation details in the same file, which I don’t think is
>>       necessarily a bad thing.
>> To summarise, it seems that the confusion the proposal brought over
>> semantics and style are not worth the limited benefits that it
>> brought. I’d be tempted to backtrack the proposal and re-introduce
>> private as a file scoped access-level and deprecate fileprivate.
>> Thoughts?
>> David.
> I agree. The minor benefit that fileprivate brings is not worth the
> cognitive overhead it introduces. We should just admit it was a
> mistake and back it out. We can avoid source-breaking changes by
> making fileprivate a synonym for private and provide fixits/warnings
> for a release to give people a chance to move off it.
> Russ
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