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

Xiaodi Wu xiaodi.wu at gmail.com
Sun Oct 16 21:23:00 CDT 2016


On that last point, I would push back against calling it access inflation.
If a member needs to be visible outside the file for whatever reason, it
needs to have at least internal visibility. This is not at all "inflated"
(implying that it's a workaround) but an explicitly contemplated part of
Swift's access scheme.

What you're arguing is that we should be able to expressly enumerate the
specific files in which a member is accessible. This is a more granular
system, but increased granularity is not in and of itself sufficient
justification. After all, if more granularity is better--and this is an
argumentum ad absurdum--why not demand that we be able to expressly
enumerate the specific types that can access that member? why not the
specific methods of those types? why not the specific scope? why not the
specific line?

It's all about what use cases are enabled or not at different points along
this spectrum of granularity. So the question is, does your proposed scheme
enable additional use cases that `internal` does not? Does it prevent some
specific harm? I'm not convinced that having access to a member at a use
site when the declaration itself is totally under your own control, in the
same module, is "brittle" is any meaningful sense.
On Mon, Oct 17, 2016 at 09:51 Jonathan Hull via swift-evolution <
swift-evolution at swift.org> wrote:

> To put it more forcefully, I believe that ‘fileprivate’ currently suffers
> from the same problem that singletons do.  That is, the main reason to make
> something ‘fileprivate’ instead of ‘private’ is to allow some sort of
> extension.  It is highly unlikely that the point you were required to
> expose for that extension will not also be needed by other extensions.
> Both ‘internal’ and submodules would extend the boundaries of the problem
> from the file boundary to the module/submodule boundary… but the underlying
> problem still persists.
>
> If it is the module designer’s intent to limit extension, then fine, but
> it also often forces a design to be much more brittle and fragile than it
> needs to be.  One of two things happens: extension becomes impossible or
> there is access inflation, giving inappropriate levels of access (usually
> combined with a note in the documentation saying not to use it).
>
> Thanks,
> Jon
>
>
> On Oct 16, 2016, at 3:28 PM, T.J. Usiyan <griotspeak at gmail.com> wrote:
>
> I don't like this at all and it comes down to  "what is hidden can also
> be unhidden". This, to me, feels like it would create more confusion than
> it would address. Why not just use `internal` for `hidden` items?  If we're
> ok with modifying import statements, why not simply have a command that
> imports `fileprivate` stuff? (not advocating for this).
>
> I think that submodules would have really helped with this issue and it is
> unfortunate that we couldn't get them in for swift 3.
>
> On Sun, Oct 16, 2016 at 4:34 PM, Jonathan Hull via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I keep wanting a “protected” access level, but I must also admit that
> there was something really elegant about Swift 2’s access scheme (and I
> think most of us feel like the word ‘fileprivate’ feels out of place).  I
> was thinking about how to mesh those two ideas, and I think I may have come
> up with a solution.
>
> I propose we replace ‘fileprivate’ with a new ‘hidden’ access level.
> Hidden would work exactly the same way as fileprivate does now, but adds
> the connotation that what is hidden can also be unhidden.  By adding
> ‘import hidden TypeName’ to another file, that file also gains access to
> all of the hidden items of that type (kind of like if it was in the same
> file).
>
> #FileA
>         import Foundation
>
>         Struct A {
>                 private var x:Int
>                 hidden var y:Int  //This is just like fileprivate, but can
> also be shared with other files
>         }
>
>         extension A {
>                 //y can be accessed here because they are in the same file
>         }
>
>
> #FileB
>         import Foundation
>         import hidden A  //This allows the entire file to see A’s hidden
> variables
>
>         extension A {
>                 //y can be accessed here because of the ‘import hidden’
> declaration
>         }
>
>
> #FileC
>         import Foundation
>
>         extension A {
>                 //y can NOT be seen or accessed here because it is hidden
>         }
>
>
> I think this is a fairly elegant solution to our protected dilemma, which
> also feels in sync with Swift 2’s file-based scheme.  The key features:
>         • Extensions no longer need to be piled in the same file if it is
> getting too long
>         • Subclasses can be in their own file, but still have access to
> the necessary parts of their superclass
>         • It communicates the author’s intent that the items are not meant
> to be visible to its users, but that it is expected to be used for
> extension/subclassing
>         • It requires an explicit statement ‘import hidden’ to access the
> hidden variables. Safe by default, with override.
>         • It is not bound by module boundaries  (i.e. you could use it for
> subclassing classes from an imported module)
>         • Roughly the same length as ‘private’ and ‘public’ so various
> declarations packed together are much easier to read (fileprivate breaks
> reading rhythm)
>
> Worth a formal proposal?
>
> Thanks,
> Jon
>
>
>
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