[swift-evolution] [Pitch] Scoped @available

[rintaro ishizaki]

2017-07-10 14:05 GMT+09:00 Xiaodi Wu <xiaodi.wu at gmail.com>:

> This would be very useful, but the spelling needs dramatic improvement.
>
> "Available unavailable" is already challenging to read, but at least it is
> learnable with time. The example where "@available(*, deprecated, access:
> internal) open" means "fileprivate" is entirely unreasonable.
>
>
I agree, but I couldn't come up with a better spelling.

// "deprecated" if the access is from "outside" of "fileprivate" scope.
@available(*, deprecated, outside: fileprivate) open

Hmm.. 🤔

Any suggestions will be greatly appreciated!



> On Sun, Jul 9, 2017 at 22:40 rintaro ishizaki via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Hi evolution community,
>>
>> I would like to propose "Scoped @available" attribute.
>>
>> What I want to achieve is to declare something that is publicly
>> unavailable, but still usable from narrower scope. A concrete example is
>> IndexableBase in the standard library:
>> https://github.com/apple/swift/blob/master/stdlib/public/cor
>> e/Collection.swift#L18-L20
>> Workaround for this problem in stdlib is to use typealias to underscored
>> declaration. However, we can't use this technique in our module because
>> underscored declarations are still visible and usable from outside.
>>
>> As a solution, I propose to add "access" parameter to @available
>> attribute, which limits the effect of @available attribute to the
>> specified value or outer.
>>
>> ---
>> // Module: Library
>>
>> /// This protocol is available for internal, but deprecated for public.
>> @available(*, deprecated, access: public, message: "it will be removed in
>> future")
>> public protocol OldProtocol {
>>     /* ... */
>> }
>>
>> public Foo: OldProtocol { // No diagnostics
>> }
>>
>> ---
>> // Module: main
>>
>> import Library
>>
>> public Bar: OldProtocol { // warning: 'OldProtocol' is deprecated: it
>> will be removed in future
>> }
>>
>> ---
>>
>> I think this is useful when you want to stop exposing declarations, but
>> want to keep using them internally.
>>
>> More examples:
>>
>> // is `open`, going to be `filerprivate`
>> @available(*, deprecated, access: internal)
>> open class Foo {}
>>
>> // was `internal`, now `private`
>> @available(*, unavailable, access: fileprivate)
>> var value: Int
>>
>> // No effect (invisible from public anyway): emit a warning
>> @available(*, unavailable, access: public)
>> internal struct Foo {}
>>
>> What do you think?
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>
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