[swift-evolution] Swift 4, stage 2 starts now

[Douglas Gregor]

> On Feb 16, 2017, at 4:18 PM, Ted Kremenek via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Stage 2
> 
> With ABI stability well-understood and many of the stage 1 goals underway, it is time to open up Swift 4 stage 2 to expand the scope of proposals to be considered.
> 
> Timeline
> 
> Stage 2 starts right now.  All design work and discussion for stage 2 extends to April 1, 2017. The intent is to timebox discussion to provide adequate time for the actual implementation of accepted proposals.
> 
> Scope
> 
> Swift 4 stage 2 builds on the goals of stage 1. It differs in that stage 2 proposals may include some additive changes and changes to existing features that don't affect the ABI. There are a few focus areas for Swift 4 stage 2:
> 
> Stage 1 proposals: Any proposal that would have been eligible for stage 1 is a priority for stage 2.
> 
> Source-breaking changes: The Swift 4 compiler will provide a source-compatibility mode to allow existing Swift 3 sources to compile, but source-breaking changes can manifest in "Swift 4" mode. That said, changes to fundamental parts of Swift's syntax or standard library APIs that breaks source code are better front-loaded into Swift 4 than delayed until later releases. Relative to Swift 3, the bar for such changes is significantly higher:
> 
> The existing syntax/API being changed must be actively harmful.
> The new syntax/API must clearly be better and not conflict with existing Swift syntax.
> There must be a reasonably automatable migration path for existing code.
> Improvements to existing Standard Library facilities: Additive changes that improve existing standard library facilities can be considered. With standard library additions in particular, proposals that provide corresponding implementations are preferred. Potential focus areas for improvement include collections (e.g., new collection algorithms) and improvements to the ergonomics of Dictionary.
> 
> Foundation improvements: We anticipate proposing some targeted improvements to Foundation API to continue the goal of making the Cocoa SDK work seamlessly in Swift. Details on the specific goals will be provided as we get started on Swift 4 stage 2.
> 

Because of the narrow scope and tight schedule, the core team will be looking at the various proposals coming in and actively deferring/closing those that are out of scope. A member of the core team will reply to the thread here on swift-evolution and/or annotate the pull request with our rationale when we do this.

	- Doug

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