[swift-evolution] private & fileprivate

Karl razielim at gmail.com
Sat Oct 8 12:02:12 CDT 2016

> On 8 Oct 2016, at 16:47, Braeden Profile <jhaezhyr12 at gmail.com> wrote:
>> On Oct 8, 2016, at 6:58 AM, Karl via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> I was thinking that the domains themselves could be associated with a domain, so you could create alternate domains which are also publicly-visible, but distinct from the default, “public” domain.
>> For example, if you have a bunch of methods which should be visible to subclasses, but you don’t want them to clutter your regular interface. Perhaps they have names which are confusingly-similar to the public API. I believe that is what “protected” is typically used for.
> Yes, but “protected" was specifically put down by the core team, seeing that any code from outside the library should see the class as one well-designed whole, not something with complicated, visible implementation details.  If your class-internal methods are confusing (and aren’t necessary for normal use), they shouldn’t be made public in any way.  Subclasses would too easily confuse the distinction between your implementation methods and your public ones.
> For what it’s worth, I was only confused by “private” and “fileprivate” for a minute or two until I looked up the actual proposal.  I haven’t had trouble with it, and it does actually provide more flexibility for code access at the file level than we had before.  Even if the syntax is clunky.

I’m not saying that (file)private is confusing - it’s very clear about what it does. But it is limiting; anything that wants access to those semi-private details needs to live in the same file. That’s clearly not scalable. Enormous files many thousands of lines long are easy for the compiler to digest, but less easy for humans to understand and navigate. In fact, I believe this whole “file-based” access control originally came out of the compiler’s implementation details.

What it would basically come down to is that the interface of the object would be separated in to blocks based on your access privileges. When viewing the interface, it wouldn’t look much different to an extension:

access(public) class TabController {
   var tabs : [Tab] { get }
   func closeTab(at: Int)

access(TabBarStuff) extension TabController {
    func close(tab: Tab)

I definitely want something between internal and fileprivate, at least. I don’t see any reason at all why objects shouldn’t be allowed to present optional “slices” of their interface to appropriate clients. In fact, that is what access control is all about. I just want to generalise it to allow for user-defined visibility scopes (as well as the default ones for public, module, file and scope). That leads to the question of what visibility those user-defined scopes would have; and if you leave them entirely open to adopt any scope (except themselves), then you end up with the ability to slice your API for different use-cases. Or we could be boring and limit them to the module they are defined in.

The whole reason I’m bringing this up is because I don’t like the “file” part of fileprivate. How I split my files up is a readability decision.

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