I think having a different default access for nested-scope adds a significant
amount of cognitive complexity for not much value. I understand that structs
as nested types are often used to communicate values outside the score
(internal even), so public will be required often in these cases. But, then
the question is what about structs that are purely for internal use, which
happens just as often? Or classes?
Furthermore, you can achieve the same level of clarity without source-breaking
changes to the language simply by better code organization, as in:
public struct MyStruct {
public var a:Int
public var b:Int
public var d:Int
private var c:Int
}
-d
> On Feb 13, 2017, at 4:02 AM, Jonathan Hull via swift-evolution
> <swift-evolution@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
>
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