Thursday, February 16, 2017

Deferring ABI Stability From Swift 4

Given the importance of getting the core ABI and the related fundamentals correct, we are going to defer the declaration of ABI stability out of Swift 4 while still focusing the majority of effort to get to the point where the ABI can be declared stable.

To allow the community to follow along with this effort, an ABI dashboard will get wired up from the swift-evolution home page that will present a table of main ABI tasks remaining and what Swift release they landed in.

[…]

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[…]

Swift 4 Release Process:

Swift 4 is a major release that is intended to be completed in the fall of 2017. It pivots around providing source stability for Swift 3 code while implementing essential feature work needed to achieve binary stability in the language. It will contain significant enhancements to the core language and Standard Library, especially in the generics system and a revamp of the String type.

[…]

The intended design is that a project containing multiple Swift modules, such as an Xcode project with multiple Swift targets, will be able to adopt into the specific Swift language mode on a per module (target) level and that they can freely interact within the same compiled binary. Note that this interoperability only exists at the binary level when the targets are compiled with the same compiler.

Postponing ABI stability (again) makes sense, especially given that String is still in flux.

Previously: Chris Lattner ATP Interview, Swift 4 String Manifesto, ABI Stability Deferred Until After Swift 3.0, Looking Back on Swift 3 and Ahead to Swift 4.

Language Design Programming Swift Programming Language