[swift-evolution] Simplifying Default Access Modifiers

Xiaodi Wu xiaodi.wu at gmail.com
Mon Feb 13 14:10:57 CST 2017

It bears mentioning that it does _not_ formally work this way with
fileprivate or private types. The default access level for members is
always internal. This was a deliberate change I suggested for SE-0025 and
is new for Swift 3. It's just also the case that the rules were relaxed to
allow you to mock up greater access for members than the containing type
(for instance, you can label members public inside a fileprivate type).

The suggestion of defaulting members to the access of the enclosing scope
was considered and rejected for the reasons enumerated already by others:
namely, that public members should always be explicitly annotated. This
becomes doubly important now that we have open as a full-fledged access
level. There is also the little problem that private in the enclosing scope
is not an utterable level in the enclosed scope, which is neatly obviated
by the fact that the default access level is internal.

On Mon, Feb 13, 2017 at 03:02 Jonathan Hull via swift-evolution <
swift-evolution at swift.org> wrote:

> I would like to propose a change to the default access modifier within an
> enclosing scope.  The default for top level definitions would stay
> internal, but anything within a scope would by default have the same
> visibility as it’s enclosing scope.
> The main reason for this is readability/maintainability, and having the
> intention clearly stand out.  It would also reduce a great amount of
> boilerplate.  It also matches the mental model of how scopes normally work
> regarding inheritance of visibility/properties (which means less to teach
> newbies).
> Right now if I want to make a type and all of it’s vars/methods public, I
> have to mark each individual var/method public, which leads to a lot of
> boilerplate/noise and makes everything harder to read:
>         public struct MyStruct {
>                 public var a:Int
>                 public var b:Int
>                 private var c:Int
>                 public var d:Int
>         }
> Notice that the private var doesn’t really stand out as such very well.
> Also, it is exceedingly rare (at least in my own coding style) that I
> actually want an internal variable unless the type itself is internal, and
> in those cases, I would like that choice to stand out as deliberate the
> same way I want ‘private' to stand out.  As it stands, I wait until I think
> I am done modifying a type to mark it public because of the extra noise
> generated.  I also make a point to write ‘internal' for things that I
> explicitly want to restrict to internal.
> Consider the alternative:
>         public struct MyStruct {
>                 var a:Int
>                 var b:Int
>                 private var c:Int
>                 var d:Int
>         }
> Now the fact that I have chosen to make ‘c’ private really stands out much
> better.  When revisiting the code in 6 months, the struct is much more
> “glance-able” (as a friend of mine likes to say).
> Note also the nuance that I didn’t say that those vars were marked public
> (or had the same modifier), I said that they had the SAME VISIBILITY as the
> enclosing scope (which in this case happens to be public).  This is a
> concept which is hard to express currently, and IIRC this is what we had to
> do to make the edge cases of swift 3’s private modifier work properly.
> Basically, it already works this way for ‘private’, ‘fileprivate’, &
> ‘internal’, just not for ‘public’ or ‘open’… which can be surprising,
> especially since you don’t discover these differences until you are working
> across modules.  We should just extend that mental model up to include
> public and open.  Migration would just take internal variables of
> public/open types and mark them explicitly with the word ‘internal'.
> Thanks,
> Jon
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
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