[swift-evolution] [Late Pitch] Deprecations, Moves, and Renames

Dave Abrahams dabrahams at apple.com
Wed Aug 10 11:24:39 CDT 2016

on Wed Aug 10 2016, Ben Rimmington <me-AT-benrimmington.com> wrote:

>> On 10 Aug 2016, at 00:36, Dave Abrahams wrote:
>>> on Tue Aug 09 2016, Ben Rimmington wrote:
>>>> On 9 Aug 2016, at 20:09, Dave Abrahams wrote:
>>>> Hi Everybody,
>>>> With another round of apologies for taking late action, we propose to
>>>> make some deprecations, moves, and renames.  The background for these
>>>> moves is as follows:
>>>> We've always known that when Swift reached ABI stability (now slated for
>>>> Swift 4), we would be committed to supporting many of the standard
>>>> library's design decisions for years to come.  What we only realized
>>>> very recently is that, although Swift 3.0 is *not* shipping with a
>>>> stable ABI, the promise that Swift 3.0 code will work with Swift 4.0
>>>> code creates similar implications when it comes to certain protocols,
>>>> today.  Especially where these protocols show up in refinement
>>>> hierarchies, we can't keep Swift 3 code working in the future without
>>>> carrying them forward into future libraries.
>>>> The proposed changes are as follows:
>>>> * Move `CustomPlaygroundQuickLookable` to the PlaygroundSupport module.
>>>> This component is really only useful for playgrounds, and doesn't
>>>> belong in the standard library.
>>> I didn't think it was possible to `import PlaygroundSupport` unless the 
>>> current file is within a playground. If so, how can corelibs-foundation 
>>> or third-party modules add `CustomPlaygroundQuickLookable`
>>> conformance?
>> Ahhh... yeah, I didn't realize that, and we don't have time to change
>> that restriction for Swift 3.  It's not a problem for
>> corelibs-foundation but it would be for 3rd-party libraries.  
>> OK, Dmitri and I just figured out how we can change the home of these
>> types for Swift 4 without breaking Swift 3 code (mirrors to the rescue!)
>> So I'm going to withdraw this part of the proposal.
> Will the following need to be reverted?
> <https://github.com/apple/swift/pull/4089>
> <https://github.com/apple/swift-xcode-playground-support/commit/aab7af4>
> <https://github.com/apple/swift-xcode-playground-support/commit/865fd0c>
> <https://github.com/apple/swift-xcode-playground-support/commit/ab605ef>
> <https://github.com/apple/swift-xcode-playground-support/commit/4bd6575>
> <https://github.com/apple/swift-xcode-playground-support/commit/acee2e1>

Technically, no, because typealiases make it unnecessary, but yes, we
plan to do that.

>>>> * Deprecate the Indexable protocols with a message indicating that they
>>>> will be gone in Swift 4.  These protocols are implementation details
>>>> of the standard library designed to work around language limitations
>>>> that we expect to be gone in Swift 4.  There's no reason for anyone to
>>>> ever touch these; users should always use a corresponding Collection
>>>> protocol (e.g. instead of MutableIndexable, use MutableCollection).
>>>> * Deprecate the ExpressibleByStringInterpolation protocol with a
>>>> message indicating that its design is expected to change.  We know
>>>> this protocol to be mis-designed
>>>> (https://bugs.swift.org/browse/SR-1260) and limited
>>>> (https://bugs.swift.org/browse/SR-2303), but there's no time to fix it
>>>> for Swift 3.  If we knew what the new design should look like, we
>>>> might be able to calculate that the current API is supportable in a
>>>> forward-compatible way (as we do for Comparable).  Unfortunately, we
>>>> do not.
>>>> * Rename Streamable to TextOutputStreamable and add a deprecated
>>>> Streamable typealias for it.  Now that OutputStream been renamed to
>>>> TextOutputStream, we should also move Streamable out of the way.
> In apple/swift#4131, these lines have overrun the 80 column limit:
> <https://github.com/apple/swift/blob/f2443f4/stdlib/public/core/Mirror.swift#L843>
> <https://github.com/apple/swift/blob/f2443f4/stdlib/public/core/Mirror.swift#L893>
> <https://github.com/apple/swift/blob/f2443f4/stdlib/public/core/Print.swift#L177>
> <https://github.com/apple/swift/blob/f2443f4/stdlib/public/core/Print.swift#L228>
> TextFormatting.rst also needs `Streamable` => `TextOutputStreamable`:
> <https://github.com/apple/swift/blob/master/docs/TextFormatting.rst>

Pull requests gratefully accepted for all of these corrections

>>>> Deprecation is being proposed instead of underscoring or renaming
>>>> because it allows existing code to keep working (with warnings).  At
>>>> this late stage, it would be bad to actually break anything.
>>> If the SE-0104 (protocol-oriented integers) proposal has been deferred, 
>>> should any protocols (e.g. SignedNumber) be deprecated?
> Will the SE-0104 proposal be accepted for Swift 4.0?

It is expected to be.  We may even be able to get it into a Swift 3
point-release (e.g. 3.1)


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