[swift-evolution] private & fileprivate

Ted F.A. van Gaalen tedvgiosdev at gmail.com
Thu Oct 13 16:27:35 CDT 2016

Please do NOT drop the current distinction between *private* and *fileprivate*
as it is now in Swift 3
It is needed for correct OOP.  

As written before, but now a bit more compact, I hope:

I would like to have the inner members of a class as default private, 
(not fileprivate)  that is, that each entity inside the class body is not visible 
in the outer scope. not even in the same file!

I would only reveal entities of a class to the outer scope that are needed.there.
(as is the case with class properties in Objective-C and most other OOP supporting languages)

This is what I have to do now,
Each and every entity that I wish to keep hidden
I have to prefix with *private*: like in this example class: 
This is tedious and should be unnecessary.

class TG3DGauge: SCNNode
    private var needles = [SCNNode]()
    private var fmtStr = “" // private should be the default!
    var value: CGFloat = 0  // access default “internal”! Visible to the outside world.
        didSet  // trigger value change, rotate needles etc.
    private var nodeUnitText = SCNNode()
    private var nodeValueText = SCNNode()
    private var valRange: ClosedRange<CGFloat> = (0...100.0)
    private var valScaleFactor: CGFloat = 1

	// etc. much more stuff here and
        // most of it should be private, that is
        // only visible within the class body!
} // end class TG3DGauge

If I don’t specify an access modifier, then the default
for the items defined in classes is *internal*,
which means that these items are visible in the whole application source.

However, this is only desirable for items that I want to
reveal explicitly, of course. 
That is exactly why I need the *private* access modifier as it is now 
and not *fileprivate*  
So I am very glad that this access modifier *private* finally became 
available in Swift 3

In my classes, *private* is probably the most used keyword, but
*private* should be the default for entities within a class body
just like it is for entities within functions.

As far as I know, prefixing with *private* is the only solution in Swift to protect
functions, vars etc. in my class against unwanted access 
from the outer scope. I think this is not the way it should be. 

Making all entities in a class private prevents this.
and offers also reasonable protection against
the Fragile Base Class problem, (thanks Chris for url) :
 https://en.wikipedia.org/wiki/Fragile_base_class <https://en.wikipedia.org/wiki/Fragile_base_class>

A solution for as it is now, albeit not a perfect one would be, 
to have some sort of access modifier which defines 
all items within the class to be private by default.
perhaps the keyword *closedscope* like in this example:

closedscope class TG3DGauge: SCNNode
    var needles = [SCNNode]()  // is now private by default
    var fmtStr = “"            // is now private by default

    public var value: CGFloat = 0 // Public!! visible outside class 
                               // “fileprivate" or “internal”  can also be used.
        didSet  // trigger value change, rotate needles etc.
    var nodeUnitText = SCNNode()  // is now private by default
    var nodeValueText = SCNNode() // is now private by default


Again, for this reasons, don’t drop the distinction between
between *fileprivate* and *private* 
if this is done, there is afaics no way to protect items within a class body.
Leave it as it is now, please. (also to prevent source breaking as well)

(btw, the above TG3DGauge class is a perfect example: 
With real gauges it would not be a good idea if one can touch
the needles and gears inside the gauge’s casing,
which is exactly the case with OOP. e.g.
In my class example people would e.g. be able to set the angle
from needles (if not declared private)  directly, without updating the value.) 

www.tedvg.com <http://www.tedvg.com/>  (see my gauges from above class here)

>> 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> <mailto: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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