[swift-evolution] Enhancing access levels without breaking changes

[David Hart]

> On 11 Apr 2017, at 16:27, Matthew Johnson <matthew at anandabits.com> wrote:
> 
> 
> 
> Sent from my iPad
> 
>> On Apr 11, 2017, at 8:53 AM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> 
>>>> On 11 Apr 2017, at 13:29, Jonathan Hull <jhull at gbis.com> wrote:
>>>> 
>>>> 
>>>> On Apr 11, 2017, at 3:53 AM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> On 11 Apr 2017, at 09:40, John McCall <rjmccall at apple.com> wrote:
>>>> 
>>>>>> On Apr 11, 2017, at 1:34 AM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>> 
>>>>>> Sent from my iPhone
>>>>>> On 11 Apr 2017, at 01:37, Ricardo Parada via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>> 
>>>>>>> I have not voted in favor or against the proposal. I have been reading a lot of responses but I agree with Tony. 
>>>>>>> 
>>>>>>> When I started reading the proposal everything was more or less fine half way through the proposal because it was reverting private to fileprivate between the type and its extensions within the same file. I said, if you think of the type and its extensions as a unit then it makes sense. I can explain that. 
>>>>>>> 
>>>>>>> Then it started describing a different behavior among the extensions located in a file separate from the file containing the definition of the type. That just started a whole debate inside my head and I understand the passionate responses on both sides. 
>>>>>>> 
>>>>>>> But then I imagined myself explaining this to someone new to Swift and it just doesn't seem right. If it becomes convoluted then that's a red flag that it does not belong in Swift. 
>>>>>> 
>>>>>> I understand what you are saying and I wouldn't be against relaxing that requirement (not talking for Chris here).
>>>>>> 
>>>>>> The model would change from "Types share scopes with their extensions in the same file the type was defined" to "Types and their extensions share the same scope in each file".
>>>>> 
>>>>> Oh, I had missed that somehow.  I agree that that is a very strange rule.  Do you know why it was proposed that way?
>>>> 
>>>> We had to take a stance and Chris seemed to prefer the rule that was proposed. I didn't press because I'm sure he has reasons for preferring it that way. But I have a preference for generalizing visibility to all extensions, even to those in a different file than the type.
>>> 
>>> I think there is a technical limitation if the visibility goes beyond the compilation unit (unless whole module optimization is turned on).
>> 
>> I’m not suggesting visibility beyond the compilation unit. That would break the hierarchy of visibility layers: accessibility levels have always been contained in one-another and that’s why you can go from private, to fileprivate, to internal, to public, to open (but not the other way round) without the risk of any compilation error. If all scopes of a type were visible to each other (whatever the file), you could not go from private to fileprivate.
>> 
>> I’m talking about extensions of the same type in the same file (but in a separate file from the type) to be able to share private members:
>> 
>> Type.swift
>> 
>> struct A {
>> }
>> 
>> Other.swift
>> 
>> extension A {
>>     func foo() {
>>         bar()
>>     }
>> }
>> 
>> extension A {
>>     private func bar() {
>>     }
>> }
> 
> If this is not how your proposal already works I missed that aspect earlier and find it extremely perplexing (which is probably why I missed it).

It's mentioned in the Derailed design section:

This proposal does not change the behavior of extensions that are not in the same file as the type - i.e., extensions in a seperate file to the type do not share access between themselves:

But I agree this should be changed if there is no major technical reason against it.

> It leaves scoped access working as in Swift 3 in exactly the case where it is least useful.  We cannot place stored properties in any extensions, let alone extensions in a file other than the one containing the original declaration.  
> 
>> 
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