[swift-evolution] private & fileprivate

[Hooman Mehr]

fileprivate  is not essential but I also would like to defend keeping it, at least for now. 

I find it useful in practice. In some cases, I can’t put a declaration in the global file scope (where fileprivate and private are essentially the same thing). For example, for organizational reasons I may have multiple protocol conformance extension blocks which use some “private” functions that are useful in more than one of those protocol extensions in the same file. 

In the future, the  introduction of submodules and having submodule-internal scope may eliminate most use cases for fileprivate. But still, we may not want the overhead of introducing submodules just to get the effect of a simple fileprivate.


> On Oct 13, 2016, at 7:44 PM, Daniel Duan via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I question the practicality of "use private heavily simply because I don’t want the burden of mixing private and fileprivate". In our experience in converting a very mature Swift application, we had no choice but to use both because we wanted private as much as possible but that's too restrictive in some cases. The granularity private and fileprivate provide is definitey a welcome change.
> 
> Daniel Duan
> Sent from my iPhone
> 
> On Oct 13, 2016, at 3:11 AM, David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> 
>>> On 13 Oct 2016, at 08:25, Jean-Daniel via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> 
>>>> Le 13 oct. 2016 à 07:52, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>>>> 
>>>> On Oct 12, 2016, at 9:56 PM, Russ Bishop via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>>>> I actually consider it very lucky that most of our changes so far have been fairly non-controversial. Everybody has a different idea of what would make Swift a better language, and all of us well-meaning. But when those ideas conflict, some group is going to end up unhappy. I'm actually very glad that (a) we haven't had too many of these cases, and (b) even when we have, people have been able to accept it and move on to contributing to the next issue.
>>>>>> 
>>>>>> 
>>>>>> Strong agreement here as well. This proposal has been litigated numerous times already, and the bar for source-breaking changes is much higher now. To effectively re-open the discussion would require a proposal that significant changes the model with a lot of evidence that such a new model is a drastic improvement over what we have now. “Back out SE-0025” is not a viable option now.
>>>>>> 
>>>>>> 	- Doug
>>>>> 
>>>>> Not really. This proposal could be backed out without source-breaking changes by treating private as a synonym for fileprivate and we’d have Swift 2 behavior without breaking source. If the core team doesn’t want to consider that then we can just move on and live with it. 
>>>> 
>>>> Not speaking for the core team, just MHO:
>>>> 
>>>> I agree with Russ here, and with others who have said upthread that the “thing that has changed” is that we are starting to get usage experience with fileprivate vs private.  I think we all understand the value of having fewer access control levels, and so if “private” isn’t conceptually pulling its weight, then it is reasonable to consider phasing it out.
>>>> 
>>>> That said, there is no specific rush to have this discussion, and I think it is reasonable to put a pretty high burden of proof on someone who wants to drive such a proposal.  For example, if we had the discussion in the spring timeframe, we should have a pretty large body of Swift 3 code readily at hand (e.g. SwiftPM packages and other various github repos).
>>>> 
>>>> Given that, it should be easy enough to see how widely private is actually being used in practice.  If it is very rare, then the argument to ditch it (make it a synonym for fileprivate, and eventually phasing out fileprivate) is strong.  If lots of people are using private and only some are using fileprivate, then the discussion is quite different.
>>>> 
>>>> -Chris
>>> 
>>> I don’t think monitoring the usage of private vs fileprivate is fair. By default, people will use private until they encounter visibility issues and discover they need to change to fileprivate. So private will probably being use far more than fileprivate.
>>> Nonetheless it does not mean people chosen private because it effectively reduce the visibility to the class scope, but just because it is easier to discover and to type than fileprivate and fit in many cases.
>>> 
>>> I tend to write class will all ivars private by default (as it is a sensible default), and then, when I start to write extensions and other parts, I have to switch to fileprivate for a bunch of ivars. It create an inconsistent mess in my ivars declaration as it is difficult to know if an ivar is private because I has to be, or because I didn’t encounter a case that need it to be fileprivate instead.
>>> 
>>> Honestly, I don’t see any value in the introduction of fileprivate.
>>> 
>>> 
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>> 
>> I also agree that monitoring the usage of private vs fileprivate is not fair. I now use private heavily simply because I don’t want the burden of mixing private and fileprivate (and find the name of fileprivate slightly verbose/ugly). But that does not mean I would vote for keeping private. I would still vote for going back to Swift 2 behaviour. But I agree that we can wait until the summer to look at this again.
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