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

[Matthew Judge]

> On Jun 28, 2016, at 22:16, Matthew Johnson <matthew at anandabits.com> wrote:
> 
> 
>>> On Jun 28, 2016, at 9:06 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> 
>>> On Jun 28, 2016, at 19:03, Matthew Judge <matthew.judge at gmail.com> wrote:
>>> 
>>> Comments inline.
>>> 
>>>> On Jun 28, 2016, at 04:14, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> Hello everybody,
>>>> 
>>>> I tried using the access rules defined in SE-0025 in some code of mine to see what effect it would have. I came out of the experiment more disappointed than I thought. Here are several reasons:
>>>> 
>>>> 1) The new rules make `private` more prominent compared to `fileprivate` (the latter has a somewhat worse name). But at the same time, the Swift community has developed a style of coding where a type is defined through a set of extensions. To hide members from other types, but have access to them inside the type extensions, we have often used `private` and placed the type and its extensions in the same file. Because `private` is scoped, we are forced into using `fileprivate` pervasively (which is uglier), using `internal` instead (which is less safe) or moving the extension code into the type's scope (which is against the way Swift code is being written today). All of these options look worse to be than before SE-0025.
>>> 
>>> If I understand SE-0025 (even with the amendment) you can still spell the access modifier to types as 'private' and get the same characteristics as the pre-SE-0025 meaning or private, so I'm not sure I understand the concern here. However (continued below)
>>>> 
>>>> 2) The new amended rules look complicated to me. I think they have the risk of being confusing in practice, but we’ll have to see.
>>>> 
>>> 
>>> I definitely agree that the amended rules look complicated. It seems to me that the amended set of rules is favoring simplifying the implementation over simplifying the mental model.
>>> 
>>> My impression of what SE-0025 decided was that 'private' meant private to the enclosing scope. If the access modifying 'private' was applied to a type at the file scope, then it was synonymous with fileprivate and the default access of members of that type should be fileprivate.
>>> 
>>> If a inner type was declared private, than the default access of members of that inner type should be private to the Outer type, not fileprivate. There is currently no way of expressing this access explicitly, but it does not seem like an especially useful thing to need to spell.
>>> 
>>> Said in code, my impression of SE-0025 is that 
>>> 
>>> private class Outer { // exactly equivalent to fileprivate
>>>     var myVar = 0 // default: fileprivate
>>>     private class Inner { // private to Outer
>>>         var hiddenVar = 0 // default: private to Outer
>>>         private var reallyHiddenVar = 0 // default private to Inner
>>>     }
>>> }
>> 
>> This is definitely one of the considered alternatives. Both Brent and I didn’t like the idea of an access level that you couldn’t actually spell, and even if we got past that, we’d still need a way to refer to it in documentation and diagnostics. I would count that as a larger change than just allowing ‘fileprivate’ in places that previously would have been called redundant.
> 
> This was really the fact that didn’t receive adequate attention during discussion and review - that the semantics everyone understood it to have implied visibility for members that you cannot state explicitly.  It didn’t bother me initially, but the diagnostics point Jordan makes is pretty important (I think we could handle it ok in documentation).  Good diagnostics are extremely important and they must be both clear and concise.  In order to have good diagnostics we need a name for the visibility that everyone knows so it may as well be part of the language.
> 

I don't want to reopen the bike shedding, but this issue was one of the main reasons I was in favor of the 'private(file)' spelling. 'private(Outer)', 'private(Inner)', etc. fall out as fairly obvious spellings for these cases in my mind.  (The only big negative I see to those spellings is the potential for confusion for anyone too used to type-based access modifiers: that something marked 'private(Outer)' would not be visible in 'extension Outer {}')

>> 
>> Jordan
>> 
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