[swift-evolution] access control proposal

[Ilya]

My main proposal was not to change the semantics of private (although I
would like that) but to introduce a way to keep class implementation
details inaccessible to anything outside the class. I think that it should
still be possible and useful to have the current level of sharing (I would
just name it differently, given what private usually means in other
languages).

Just as it is convenient to group several related classes that can refer to
each other's implementation details, it is very convenient to have several
classes that don't do this but are still related in other important way,
for example related APIs or classes that are based on the same
implementation idea (like array based data structures).

Having all code in one place rather than jumping through many small files
is a very nice thing to have because it really helps to keep everything
consistent. The more manual work people have to do for consistency, the
more likelihood that it won't be done.

--
Ilya Belenkiy
On Mon, Dec 7, 2015 at 12:21 AM John McCall <rjmccall at apple.com> wrote:

>
> > On Dec 5, 2015, at 8:39 PM, Ilya via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > I think the it would help a great deal to have an access level modifier
> that is really private and visible only inside the class itself. Right now,
> the only way to hide implementation details for a class is to hide the
> class code in a separate file, which is very inconvenient for several
> reasons:
> >
> > 1) the meaning of the code changes depending on which file the class is
> in. It's very easy to accidentally expose class internal details and then
> call class elements that are meant to be used only inside the class. Having
> a keyword for class internals will allow the compiler to ensure that only
> the public API for the class is used from the outside world. The user can
> check types on his own, but it's better that the compiler does it
> automatically. Similarly, the user can check that only the proper APIs are
> called, but it's better that the compiler does it automatically.
> >
> > 2) accessibility by file structure may cause some really short files.
> >
> > 3) It's impossible to group related classes in one file but still hide
> implementation details inside each class
> >
> > I think that it the best solution is to make private keyword do what it
> states -- keep the class element private to the class. But if it's really
> important to have a separate keyword for backward compatibility, it would
> be the next best thing.
>
> But on the flip side, with your proposed semantics for private, it would
> be impossible to write a group of related types, functions, and extensions
> that do need to refer to each other’s internal details without exposing
> those details to the entire module.  That’s not really acceptable.
>
> The Swift language rule encourages you to put independent definitions in
> different files.  That definitely means that, if you want to enforce very
> tight separation of concerns, you’ll end up with more and smaller files.
> You haven’t explained why that’s really a *problem*, though.
>
> John.
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