This maintains proposals for changes and user-visible enhancements to the Swift Programming Language.

Swift Programming Language Evolution

Before you initiate a pull request, please read the process document. Ideas should be thoroughly discussed on the swift-evolution mailing list first.

This repository tracks the ongoing evolution of Swift. It contains:

This document describes goals for the Swift language on a per-release basis, usually listing minor releases adding to the currently shipping version and one major release out. Each release will have many smaller features or changes independent of these larger goals, and not all goals are reached for each release.

Goals for past versions are included at the bottom of the document for historical purposes, but are not necessarily indicative of the features shipped. The release notes for each shipped version are the definitive list of notable changes in each release.

Development major version: Swift 3.0

Expected release date: Late 2016

The primary goal of this release is to solidify and mature the Swift language and development experience. While source breaking changes to the language have been the norm for Swift 1 through 3, we would like the Swift 3.x (and Swift 4+) languages to be as source compatible with Swift 3.0 as reasonably possible. However, this will still be best-effort: if there is a really good reason to make a breaking change beyond Swift 3, we will consider it and find the least invasive way to roll out that change (e.g. by having a long deprecation cycle).

To achieve this end, Swift 3 focuses on getting the basics right for the long term:

  • API design guidelines: The way in which Swift is used in popular libraries has almost as much of an effect on the character of Swift code as the Swift language itself. The API naming and design guidelines are a carefully crafted set of guidelines for building great Swift APIs.

  • Automatic application of naming guidelines to imported Objective-C APIs: When importing Objective-C APIs, the Swift 3 compiler automatically maps methods into the new Swift 3 naming guidelines, and provides a number of Objective-C features to control and adapt this importing.

  • Adoption of naming guidelines in key APIs: The Swift Standard Library has been significantly overhauled to embrace these guidelines, and key libraries like Foundation and libdispatch have seen major updates, which provide the consistent development experience we seek.

  • Swiftification of imported Objective-C APIs: Beyond the naming guidelines, Swift 3 provides an improved experience for working with Objective-C APIs. This includes importing Objective-C generic classes, providing the ability to import C APIs into an “Object Oriented” style, much nicer imported string enums, safer syntax to work with selectors and keypaths, etc.

  • Focus and refine the language: Since Swift 3 is the last release to make major source breaking changes, it is also the right release to reevaluate the syntax and semantics of the core language. This means that some obscure or problematic features will be removed, we focus on improving consistency of syntax in many small ways (e.g. by revising handling of parameter labels, and focus on forward looking improvements to the type system. This serves the overall goal of making Swift a simpler, more predictable, and more consistent language over the long term.

  • Improvements to tooling quality: The overall quality of the compiler is really important to us: it directly affects the joy of developing in Swift. Swift 3 focuses on fixing bugs in the compiler and IDE features, improving the speed of compile times and incremental builds, improving the performance of the generated code, improving the precision of error and warning messages, etc.

One of the reasons that stability is important is that portability to non-Apple systems is also a strong goal of Swift 3. This release enables broad scale adoption across multiple platforms, including significant functionality in the Swift core libraries (Foundation, libdispatch, XCTest, etc). A useful Linux/x86 port is already available (enabling many interesting server-side scenarios), and work is underway across the community to bring Swift to FreeBSD, Raspberry Pi, Android, Windows, and others. While we don’t know which platforms will reach a useful state by the launch of Swift 3, significant effort continues to go into making the compiler and runtime as portable as practically possible.

Finally, Swift 3 also includes a mix of relatively small but important additions to the language and standard library that make solving common problems easier and make everything feel nicer. A detailed list of accepted proposals is included below:

Implemented proposals for Swift 3

Accepted proposals which do not have a complete implementation

This is the list of proposals which have been accepted for inclusion into Swift, but they are not implemented yet, and may not have anyone signed up to implement them. If they are not implemented in time for Swift 3, they will roll into a subsequent release.

Swift 2.2 - Released on March 21, 2016

This release focused on fixing bugs, improving quality-of-implementation (QoI) with better warnings and diagnostics, improving compile times, and improving performance. It put some finishing touches on features introduced in Swift 2.0, and included some small additive features that don’t break Swift code or fundamentally change the way Swift is used. As a step toward Swift 3, it introduced warnings about upcoming source-incompatible changes in Swift 3 so that users can begin migrating their code sooner.

Aside from warnings, a major goal of this release was to be as source compatible as practical with Swift 2.0.

Implemented proposals in Swift 2.2

Other Proposals

Rejected or withdrawn proposals


Swift Evolution Review Schedule

Returned for Revision

Deferred for Future Discussion

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