[swift-evolution] Type-based ‘private’ access within a file

Vladimir.S svabox at gmail.com
Wed Apr 5 06:31:20 CDT 2017

On 05.04.2017 7:02, Chris Lattner via swift-evolution wrote:
> On Apr 3, 2017, at 11:34 AM, Douglas Gregor via swift-evolution
> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Hello Swift Community,
>> In rejecting SE-0159
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md>,
>> the core team described a potential direction we would like to
>> investigate for “private” access control that admits a limited form of
>> type-based access control within files. The core team is seeking some
>> discussion here and a motivated volunteer to put together a proposal
>> along these lines for review in the Swift 4 time-frame (i.e., very soon).
>> To be clear, the core team it’s sure this is the right direction to go…
>> but it appears promising and we would *love* to be able to settle the
>> access-control issue.
>> The design, specifically, is that a “private” member declared within a
>> type “X” or an extension thereof would be accessible from:
>> * An extension of “X” in the same file
>> * The definition of “X”, if it occurs in the same file
>> * A nested type (or extension thereof) of one of the above that occurs in
>> the same file
> Another way to explain this is as a relaxation of the Swift 3 access
> control, to would allow private members in a type to also be accessible in
> extensions to that type, so long as they are in the same file.
> While I typically try to avoid chiming in on early discussions like this, I
> pretty strongly believe that this is a good solution for the reasons you
> mention:
>  - fileprivate should really become much more rare, which makes it more
> meaningful and significant where it occurs.  This was the original idea and
> intent behind SE-0025.
>  - Similarly, this simplifies access control for most people.  Most people
> will now only care about private/internal/public.  fileprivate will become
> an expert feature used in specific cases to solve a specific class of
> problems.  Progressive disclosure of complexity is important.
>  - This design is true to the existing design of Swift: we want to
> encourage the implementation of types to be freely broken into extensions.
>  This alignment with extension oriented programming was the one important
> virtue of the Swift 1/2 access control design that Swift 3 lost.
> From a pragmatic perspective, I feel like this is a great solution that
> really does solve the problems we have with current access control, all
> without breaking source compatibility.  This is also a major progression
> from where we are, and doesn’t appear to cut off any future directions
> (e.g. submodules) since those are cross-file concepts that live between
> internal/public or between fileprivate/internal.

If we have Swift2's 'private' (instead of fileprivate) and 'scoped'(instead 
of current 'private'), then such 'private' can naturally mean "private to 
submodule" *especially* if file will be treated as un-named submodule.

What we'll have with 'fileprivate' to have a submodule-wide access? New 
keyword 'submoduleprivate' ? Will extend meaning of proposed 'private' ? 
Rename 'fileprivate' to something else?
Just wonder if this direction was really discussed and core team has some 
thoughts about this.

> Just MHO, but I think that the rhetorical attempts to paint this as being
> similar to “protected” are unsound.
> -Chris
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