[swift-evolution] [Discussion] A Problem With SE-0025?

[Matthew Johnson]

Sent from my iPad

On Jun 16, 2016, at 5:20 AM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:

>> 6. With the core team tied up at WWDC, you may want to temporarily forbid the use of `private` on a type and revisit the matter when people are less busy; if necessary, we could even ship Swift 3 that way. Or you may want to consider making a guess as to a good implementation model to apply. Two suggestions for alternate implementation models:
>> 
>> a. Introduce a `parent` access level, meaning "visible in scopes within this file where the parent is visible", which is between `fileprivate` and `private`. Just as `internal` is the maximum inherited access level, `parent` is the minimum, so the members of a `private` type would inherit `parent` visibility. `parent` might be an entirely compiler-internal concept, with no utterable access control keyword.
> 
> Thinking about this more, I notice that `fileprivate` as currently defined doesn't actually make any sense to say inside a `private` type: if your parent type has less-than-file-wide visibility, nothing in the file that's outside its scope can see you anyway. Therefore, we could redefine `fileprivate` thusly:
> 
>    1. A member with `fileprivate` visibility is visible within the scope in which the nearest containing `private` type is visible.
>    2. If there are no containing `private` types, it is visible within the file containing it.
>    3. Just as the members of a `public` type are `internal`, so the members of a `private` type are `fileprivate`.
> 
> This kind of suggests that we ought to rename `fileprivate` to something that, y'know, doesn't say "file" in it. However, I can scarcely imagine the results of a round of bikeshedding without parental supervision from the core team, so I don't dare make any suggestions.

I am not convinced this is necessary.  If there *is* a containing 'private' scope you can just leave the member unannotated to get this behavior.  If there isn't you can use 'fileprivate' as it is already defined.  Why is that not sufficient?

If you really want a second, more nuanced and complex scope-dependent access control mechanism I think you'll need to submit a proposal for it.  A simple renaming to 'fileprivate' is what has been accepted thus far.  

The main argument for what you suggest is that it would provide a way to ensure visibility of the member is*never* more than the file, but is as visible as possible within the file, while being less sensitive to changes in visibility of surrounding scopes.  IMO we need to get some experience with SE-0025 in real code before we know whether this is a problem that needs solving or not.

-Matthew

> 
> -- 
> Brent Royal-Gordon
> Architechies
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution