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

[Charles Srstka]

> On Mar 21, 2017, at 5:26 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
> 
> So, if four/five access modifiers are too many, which one is carrying the least weight? Which one could be removed to simplify the scheme while maintaining the most expressiveness? Which one doesn't fulfill even its own stated goals? Well, one of the key goals of `private` was to allow members to be encapsulated within an extension, hidden even from the type being extended (and vice versa for members defined in the type). It says so in the first sentence of SE-0025. As seen above in my discussion with Charles Srstka, even supporters of `private` disagree with that motivation to begin with. The kicker is, _it also doesn't work_. Try, for instance:
> 
> ```
> struct Foo {
>   private var bar: Int { return 42 }
> }
> 
> extension Foo {
>   private var bar: Int { return 43 }
> }
> ```
> 
> The code above should compile and does not. If I understood correctly the explanation from a core team member on this list, it's unclear if it can be made to work without changing how mangling works, which I believe impacts ABI and is not trivial at all. Thus, (a) even proponents of new `private` disagree on one of two key goals stated for new `private`; (b) that goal was never accomplished, and making it work is not trivial; (c) no one even complained about it, suggesting that it was a low-yield goal in the first place.

Multiple people have already brought up cases in which they are using ‘private’. The repeated mention of another, unrelated use case that was mentioned in the SE-0025 proposal does not invalidate the real-world use cases which have been presented. In fact, it rather makes it appear as if the motivation to remove ‘private’ is based on a strange invocation of the appeal-to-authority fallacy, rather than an actual improvement to the language.

Many people used to argue against early returns as being tantamount to littering one’s code with GOTO statements willy-nilly, instead advocating for assigning to a return variable which would then be returned in the last line of the function. Swift explicitly rejects this view, offering constructs such as the guard statement and the error-handling mechanism which specifically encourage early returns. However, I don’t see people using the non-acceptance of this particular argument against GOTOs as an argument for eliminating all structured flow control from the language.

Charles

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