[swift-evolution] Type-based ‘private’ access within a file

[Charles Srstka]

> On Apr 5, 2017, at 6:10 PM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On Apr 5, 2017, at 2:27 PM, Tony Arnold via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> I know Swift has different purposes for different people here, but ultimately it’s supposed to support great application development for Apple’s platforms, right? To my eyes, `fileprivate` should never have been introduced without some kind of `typeprivate` (similar to how things would be declared back in Objective-C land with a `*+Private.h` header that you could import when it was needed). Right now, there’s no way to duplicate that pattern in Swift - I would need to make anything I wish to access `internal` which exposes it to everything within the application/module - surprisingly, this is a regression from the tooling and access levels I had available in Objective-C. 
> 
> 
> If our goal was to duplicate what Objective-C could do but without header files, we would essentially have:
> 
> * `public`
> * `internal`
> * `semiprivate`
> * `fileprivate`
> 
> Symbols in `semiprivate` scope would be visible to the file they were in as well as any file that explicitly asked for access to `semiprivate` symbols in that file. (In practice, I think we'd probably tie `semiprivate` to submodules, not to files, though submodule membership might not have a granularity below full files.)
> 
> There would be no scoped `private` or `typeprivate` or anything of the sort. That just isn't a thing that existed in Objective-C. So I'm not sure why you're invoking Objective-C to argue that we need a type-based private.

Because while it was technically possible for any file that wanted to to include the private header, in *practice* this was often used to implement ‘typeprivate’-like functionality.

Charles

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