[swift-evolution] SE-0025: Scoped Access Level, next steps

Ilya Belenkiy ilya.belenkiy at gmail.com
Thu Mar 24 09:59:33 CDT 2016 

I am not sure if consistency is a problem here. My primary concern is that
as long as the class or extension code itself hasn't changed, it's private
API stays hidden from anything else. If we can simply inject a class into a
class or extension and get access to all of its internals, that reduces the
protection level that private would provide. I'd like private to hide
implementation details completely.

That said, I am not sure if we need to discuss it as part of this proposal.
On Thu, Mar 24, 2016 at 10:28 AM Matthew Johnson <matthew at anandabits.com>
wrote:

>
>
> Sent from my iPad
>
> On Mar 24, 2016, at 8:40 AM, Ilya Belenkiy <ilya.belenkiy at gmail.com>
> wrote:
>
> The discussion was about the other direction: whether a nested class
> should have access to private members of the outer class.
>
>
> In that case the answer seems clear as well.  Everywhere in Swift's access
> model nested scopes have visibility to all members visible in the
> containing scope.  For example, all scopes in a file can see any
> "fileprivate" members contained in that file.
>
> Following this semantic, all nested types would be able to see members of
> their containing type, even those with the new "private" visibility because
> the nested types are within the same scope where those members are
> declared.
>
> Semantic consistency is the most important concern IMO.  All current
> access modifiers are strictly based on nested scopes.  Hiding members of a
> containing type from a nested type would break this model and introduce
> type-driven semantics, which I think (and hope) is beyond the scope of this
> proposal (pun mildly intended).
>
> Matthew
>
>
> On Thu, Mar 24, 2016 at 9:35 AM Matthew Johnson <matthew at anandabits.com>
> wrote:
>
>>
>>
>> Sent from my iPad
>>
>> On Mar 24, 2016, at 5:07 AM, Ilya Belenkiy via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>> It's very consistent with other keywords. I wish compound keywords were
>> joined with a dash or something that made them easier to read, but I guess
>> it's too late now. If we have associatedtype, it makes sense to use
>> moduleprivate (I saw that the name associatedtype was discussed extensively
>> but didn't participate in the discussion; I am sure that it was given a lot
>> of thought). If we could change this, I'd suggest keyword names with dashes
>> everywhere, but if not, these names work well and is a great compromise for
>> everything I've seen in this thread.
>>
>> I am not worried about the length because the 2 most frequently written
>> keywords would be public and private. Moduleprivate is the default, and
>> file private will not be used as often as private.
>>
>> One question: should the proposal be explicit about access control for
>> nested classes? We discussed it here briefly (I wanted private to be
>> completely private to the class or extension itself while 2 other people
>> wanted a nested class to have access to the outer class.)
>>
>>
>> I don't think it would make sense at all to allow an outer type to see
>> private members of a nested class.  That would break the semantics of
>> private meaning "containing scope".
>>
>> However, with Chris's suggestion of using identifiers as parameters,
>> maybe we could eventually have something like private(OuterTypeName) to
>> specify the precise level of access desired.
>>
>>
>> On Thu, Mar 24, 2016 at 1:13 AM Chris Lattner via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>> <responding to several posts in this thread at once>
>>>
>>> On Mar 14, 2016, at 5:18 PM, Chris Lattner via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>> > Per Doug’s email, the core team agrees we should make a change here,
>>> but would like some bikeshedding to happen on the replacement name for
>>> private.
>>>
>>> What we do with private setters is orthogonal from this proposal, so I’m
>>> going to ignore it in this thread.  After SE-0025 is resolved, it would be
>>> great to have another thread/proposal that discusses reskinning
>>> private(set) - presumably as just a modifier on the setter.
>>>
>>> Similarly, this proposal has nothing to do with “protected” or any other
>>> type based access control, so I don’t delve into that at all either.
>>>
>>> I’ve seen several proposals that seem promising:
>>>
>>> On Mar 14, 2016, at 5:49 PM, James Berry <jberry at rogueorbit.com> wrote:
>>> > I like fileprivate, if that’s the only change. On the other hand, if
>>> we want to consider a broader change, what about:
>>> >
>>> >       private                 symbol visible within the current
>>> declaration (class, extension, etc).
>>> >       private(module) symbol visible within the current module.
>>> >       private(file)           symbol visible within the current file.
>>>
>>> I love how this establishes a family with different levels of access
>>> control, and unites them under the idea of "levels of being private”.  I
>>> also like how people would commonly only ever write public and private
>>> (because “private(module)” is the default, and "private(file)" is
>>> obscure).  However, parenthesized modifiers that take a keyword (as opposed
>>> to an identifier) are a bit weird and awkward, so it would be nice to avoid
>>> them if possible.
>>>
>>> On Mar 15, 2016, at 3:39 AM, Thorsten Seitz via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>> > public
>>> > private-module
>>> > private-file
>>> > private
>>>
>>> This follows the same sort of structure as James’ proposal, without the
>>> parens.  It has the same advantages, but trades them with hyphenated decl
>>> modifiers.  We don’t do that, but it is a good direction.
>>>
>>> How about we continue this trend, and follow other existing Swift
>>> keywords that merge two lowercase words (associatedtype, typealias, etc),
>>> and use:
>>>
>>>         public
>>>         moduleprivate
>>>         fileprivate
>>>         private
>>>
>>> The advantages, as I see them are:
>>> 1) We keep public and private meaning the “right” and “obvious” things.
>>> 2) The declmodifiers “read” correctly.
>>> 3) The unusual ones (moduleprivate and fileprivate) don’t use the
>>> awkward parenthesized keyword approach.
>>> 4) The unusual ones would be “googable”.
>>> 5) Support for named submodules could be “dropped in” by putting the
>>> submodule name/path in parens: private(foo.bar.baz) or
>>> moduleprivate(foo.bar).  Putting an identifier in the parens is much more
>>> natural than putting keywords in parens.
>>>
>>> What do you all think?
>>>
>>> -Chris
>>>
>>>
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