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

[Matthew Johnson]

Sent from my iPad

> On Jun 15, 2016, at 1:51 PM, Robert Widmann <devteam.codafi at gmail.com> wrote:
> 
> Then it is no different from fileprivate.

Yes, at file scope this is true.  A reasonable argument can be made for prohibiting it at file scope for the sake of clarity, but if it is allowed it should behave the same as fileprivate.

Note that similar issues apply for nests types:

struct S {
    private struct T { 
        var foo: Int
    }
    // ok - T and foo are visible inside the scope of S
    private var t = T(foo: 42)
}

> 
> ~Robert Widmann
> 
> 2016/06/15 11:47、Matthew Johnson <matthew at anandabits.com> のメッセージ:
> 
>> 
>>> On Jun 15, 2016, at 1:37 PM, Robert Widmann <devteam.codafi at gmail.com> wrote:
>>> 
>>> The scope of the *declaration* is not the issue.  The scope of its *members* is.
>> 
>> Let’s consider an example:
>> 
>> private struct Foo {
>>   var bar: Int
>> }
>> 
>> // elsewhere in the same file:
>> var foo = Foo(bar: 42)
>> foo.bar = 44
>> 
>> `Foo` is declared private.  Private for this declaration is at the file scope.  The `bar` member has no access modifier so it has the same visibility as the struct itself, which is file scope.  This will also be true of the implicitly synthesized memberwise initializer.  
>> 
>> This means that it is possible to initialize `foo` with a newly constructed instance of `Foo` and to modify the `bar` member anywhere else in the same file.
>> 
>> If `bar` was also declared `private` this would not be possible as its visibility would be restricted to the surrounding scope of the initial declaration of `Foo`.  This means `Foo` would need to provide an explicit initializer or factory method with `fileprivate` visibility in order to be usable.
>> 
>> Members with no explicit access modifier should have the same *visibility* as their containing type (with a maximum implicit visibility of internal), not the same *modifier* as their containing type.  The only case where there is a distinction is the new `private` visibility.  Maybe that is what is causing the confusion?
>> 
>> Does this help?
>> 
>> -Matthew
>> 
>>> 
>>> ~Robert Widmann
>>> 
>>> 2016/06/15 11:36、Matthew Johnson <matthew at anandabits.com> のメッセージ:
>>> 
>>>> The scope for a top-level declaration is the file itself.  This means that top-level declarations with `private` and `fileprivate` should have the same behavior.  They should not be uninstantiable or unusable.
>>>> 
>>>> -Matthew
>>>> 
>>>>> On Jun 15, 2016, at 1:31 PM, Robert Widmann via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> 
>>>>> While implementing SE-0025 (fileprivate), I noticed an interesting bug in the proposal.  Under the implementation outlined there, any top-level structure, class, or enum declared private cannot possibly be instantiated and so cannot be used in any way.  Because of this, private top-level declarations are more often than not blown away entirely by the compiler for being unused.  It seems strange to me to allow a key language feature to act solely as a hint to the optimizer to reduce the size of your binary.  Perhaps the restrictions around private needs to be relaxed or the line between fileprivate and private needs to be investigated again by the community before inclusion in the language.
>>>>> 
>>>>> Thoughts?
>>>>> 
>>>>> ~Robert Widmann
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>>