[swift-evolution] access control proposal

Marc Knaup marc at knaup.koeln
Mon Dec 14 11:05:14 CST 2015

Isn't declaring "scope" access for a type at file-level effectively the
same as "internal"?
All symbols I declare at top-level of a file have "internal" access by

For me "public", "internal" and "private" ARE access *scopes* so adding
"scope" as an additional access scope is somehow confusing.

On Mon, Dec 14, 2015 at 5:58 PM, Matthew Johnson via swift-evolution <
swift-evolution at swift.org> wrote:

> I agree that you can concoct arbitrarily complex scenarios and a line must
> be drawn somewhere.  IMO the best place to draw the line is when you start
> considering something that is not super straightforward to explain and is
> not a natural extension of the obviously necessary access modifiers.
> IMO ‘scope’ passes this test and all of the complex counter-examples do
> not.  It is the logical conclusion of a simple narrowing of visibility from
> “everyone” to “module” to “file” to “scope”.  It is simple to explain and
> understand.  Those who don’t like it don’t need to use it.  Anything more
> complex is unlikely to pass such a test.
> Matthew
> On Dec 14, 2015, at 10:52 AM, David Owens II <david at owensd.io> wrote:
> Let’s take this it’s next logical conclusion: I have two types that need
> to access each other’s members for some significant performance gain. Let’s
> call these types A and B. Now, A also needs access to the inner members for
> C for the same reason (but note that B does not). I currently have other
> related types all in the same file, let’s say D and E.
> Now, all members should be “local” to the types, but remember, A needs to
> access B's and C's members and the other types do not. Also, I can’t simply
> move the them to different files because they have non-overlapping “local”
> usage requirements. So do I need to create a “local friend” modifier so
> only particular types can access the inner details?
> There’s a line somewhere where complexity becomes more burdensome. I’m not
> sure if “local” is that line, but I absolutely do know that “local friend”
> is across that line (because of course we’ll need private friend and
> internal friend modifiers as well…).
> I imagine physical layout like this is not uncommon in Swift code.  This
> does not necessarily mean you want these extensions to see implementation
> details of each other.  By adding a ‘scope’ access modifier we are able to
> properly hide these implementation details regardless of physical layout.
> As mentioned above, what if you only want to make them available to *some* of
> the extensions?
> -David
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