[swift-evolution] Replace Fileprivate with Hidden + Import Hidden

Jay Abbott jay at abbott.me.uk
Mon Oct 17 07:47:06 CDT 2016

Oops, correction:

@unshelter<Wotsits>(self); or
// Inside a Wotsit or a Wotsit subclass this would work, y becomes

Should be:

// Inside a Wotsit or a Wotsit subclass this would work, y becomes

On Mon, 17 Oct 2016 at 13:38 Jay Abbott <jay at abbott.me.uk> wrote:

> I'm not sure of my own opinions on this one as I can see good points on
> both sides. There also seem to be a variety of different discussions with
> similar concerns. So at the risk of confusing things I'm suggesting another
> idea, with the hope/intention of promoting some deeper thought and helping
> us figure out what is needed/wanted.
> I will use the word 'sheltered' here, apologies if that is confusing, it
> just means protected/hidden/whatever but without any existing notions of
> what those might mean. It might not be the best word either, I just picked
> it from a list of synonyms for 'protected'.
> Class authors can (now) if they want provide their own way to explicitly
> access some private members through a public interface:
> public class Thing {
>     private var x: Int
>     public var shelteredX: Int {
>         get { return x }
>         set { x = newValue }
>     }
> }
> But this isn't ideal as it just causes excess boilerplate code and doesn't
> hide it from anyone or suggest they shouldn't normally use it (other than
> the explicit naming). However, perhaps the compiler could help with this
> type of pattern as follows:
> public class Thing {
>     sheltered var x: Int {
>         get { return x } // not sure how this would work - x is also the
> backing ivar so you don't have to declare it twice as _x and x.
>         set { x = newValue }
>     }
>    // accessors provided - internal access to x is direct, sheltered
> access is via accessors
>     sheltered var y: Int
>     // No accessors provided, sheltered access to y is direct
> }
> For members with 'sheltered' access:
> * Don't by default allow access to the sheltered members or accessors -
> they are equivalent to private (or maybe fileprivate)
> * Provide a way to expose them in a given scope
> * I think it can be applied to methods too
> For example:
> var aThing = Thing()
> aThing.x = 7 // NOT ALLOWED: x is sheltered.
> @unshelter(aThing) // aThing is unsheltered in the remainder of its scope.
> aThing.x = 7 // NOW ALLOWED
> One good thing is that this is very explicit where you use it.
> Sheltered groups might also be a thing:
> Definition:
> sheltered<Subclasses> var x: Int
> sheltered<Wotsits> var y: Int
> Usage:
> @unshelter<Subclasses>(aThing)
> // x is available, y isn't
> @unshelter<Subclasses, Wotsits>(aThing)
> // x and y are available
> "Subclasses" and "Wotsits" are author-defined identifiers, not keywords.
> This is a bit like friends and protected, but using an honesty system,
> where friends can easily declare themselves as friends by unsheltering all
> the Wotsits group, and subclasses (not enforced) would unshelter the
> Subclasses group. That is, the author's intentions are clear, but other
> classes can abuse it to get access. If the author doesn't want to allow
> abuse, they can do this:
> Definition:
> sheltered<Subclasses: Thing> var x: Int
> sheltered<Wotsits: Wotsit> var y: Int
> Usage:
> @unshelter<Subclasses>(self); or
> @unshelter<Subclasses>(anOtherThing)
> // Works inside a Thing subclass, x becomes available. The scope in which
> @unshelter is used must match the type of the shelter group.
> @unshelter<Wotsits>(self); or
> @unshelter<Wotsits>(aWotsit)
> // Inside a Wotsit or a Wotsit subclass this would work, y becomes
> available.
> I'm just spitballing here, this isn't fully thought through. Perhaps a
> where clause would be better instead of a type annotation for the shelter
> groups, so you could list multiple types that are allowed to unshelter that
> group. You might be able to abuse it still by putting something in an
> extension of an allowed class, so that may need some further thought.
> This is of course more complex that other proposed solutions, I'm just
> trying to combine all the desires people seem to have and see what people
> think - do we want more control and are happy with a bit more complexity?
> or should it be simple and less control? Personally I actually don't have
> much of an opinion on it because I haven't used Swift enough yet to come a
> cropper of such things.
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