View source for Swift (programming language)

{{Short description|General-purpose compiled programming language}}

{{Infobox programming language
| name = Swift (programming language)
| title = Swift
| logo = File:Swift logo.svg
| logo caption = Logo
| logo size = 200px
| paradigm = Multi-paradigm: [[Protocol (object-oriented programming)|protocol-oriented]], [[Object-oriented programming|object-oriented]], [[Functional programming|functional]], [[Imperative programming|imperative]], [[Block (programming)|block structured]], [[Declarative programming|declarative]], concurrent
| released = {{start date and age|2014|6|2}}<ref name=version1>{{cite web |access-date=March 8, 2015 |url=https://developer.apple.com/swift/blog/?id=14 |title= Swift Has Reached 1.0 |publisher=Apple |date=September 9, 2014 }}</ref>
| designer = [[Biography:Chris Lattner|Chris Lattner]], Doug Gregor, John McCall, Ted Kremenek, Joe Groff, and [[Company:Apple Inc.|Apple Inc.]]<ref>U.S. patent no. 9329844</ref>
| developer = [[Company:Apple Inc.|Apple Inc.]] and open-source contributors
| latest_release_version = {{wikidata|property|reference|edit|Q17118377|P348}}
| latest_release_date = {{start date and age|{{wikidata|qualifier|single|Q17118377|P348|P577}}}}
| latest preview version = 5.9
| latest preview date = 
| typing = [[Type system#Static type-checking|Static]], strong, [[Type inference|inferred]]
| memory management = [[Automatic Reference Counting]]
| operating system = Apple's operating systems ([[Software:Darwin (operating system)|Darwin]], [[Software:IOS|iOS]], [[Software:IPadOS|iPadOS]], [[Software:MacOS|macOS]], [[Software:TvOS|tvOS]], [[Software:WatchOS|watchOS]]), [[Software:Linux|Linux]], [[Software:Windows|Windows]], [[Software:Android (operating system)|Android]]
| website = {{plainlist|
*{{URL|https://www.swift.org/}}
*{{URL|https://developer.apple.com/swift/}}
}}
| file ext = .swift, .SWIFT
| influenced = [[Rust (programming language)|Rust]],<ref>{{cite web |url=https://doc.rust-lang.org/reference/influences.html |title=Influences - The Rust Reference |date=<!--Undated--> |author=<!--Not stated--> |website=doc.rust-lang.org |access-date=2020-05-02}}</ref> [[V (programming language)|V (Vlang)]]<ref>{{cite web |url=https://github.com/vlang/v/blob/master/doc/docs.md#introduction |title=influenced by - V documentation |date=<!--Undated--> |author=<!--Not stated--> | website=github.com |access-date=2023-11-03}}</ref>
}}

'''Swift''' is a [[High-level programming language|high-level]] [[General-purpose programming language|general-purpose]], multi-paradigm, [[Compiled language|compiled]] [[Programming language|programming language]] developed by [[Company:Apple Inc.|Apple Inc.]] and the open-source community. Swift compiles to machine code, as it is an [[Software:LLVM|LLVM]]-based compiler. Swift was first released in June 2014,<ref>{{Cite web |last=Lardinois |first=Frederic |date=2014-06-02 |title=Apple Launches Swift, A New Programming Language For Writing iOS And OS X Apps |url=https://techcrunch.com/2014/06/02/apple-launches-swift-a-new-programming-language-for-writing-ios-and-os-x-apps/ |access-date=2022-09-07 |website=TechCrunch |language=en-US}}</ref> and the Swift toolchain has shipped in [[Software:Xcode|Xcode]] since version 6, released in 2014.

Apple intended Swift to support many core concepts associated with [[Objective-C]], notably [[Dynamic dispatch|dynamic dispatch]], widespread [[Late binding|late binding]], [[Extensible programming|extensible programming]] and similar features, but in a "safer" way, making it easier to catch software bugs; Swift has features addressing some common programming errors like [[Null pointer|null pointer]] [[Dereference operator|dereferencing]] and provides [[Syntactic sugar|syntactic sugar]] to help avoid the [[Pyramid of doom (programming)|pyramid of doom]]. Swift supports the concept of [[Protocol (object-oriented programming)|protocol]] extensibility, an extensibility system that can be applied to types, [[Record (computer science)|structs]] and [[Class (computer programming)|classes]], which Apple promotes as a real change in programming paradigms they term "protocol-oriented programming"<ref>{{cite AV media |url=https://www.youtube.com/watch?v=g2LwFZatfTI |title= Protocol-oriented Programming in Swift |publisher=[[Company:YouTube|YouTube]]|work=Apple Inc.}}</ref> (similar to [[Trait (computer programming)|traits]] and [[Type class|type class]]es).<ref>{{cite web|url=https://news.ycombinator.com/item?id=13225740|title=Concepts are similar to Rust Traits}}</ref>

Swift was introduced at Apple's 2014 Worldwide Developers Conference (WWDC).<ref name="tnw swift info 1">{{cite web|url=https://thenextweb.com/apple/2014/06/02/apple-announces-swift-new-programming-language-ios|title=Tim Berners-Lee's sixtieth birthday Apple announces Swift, a new programming language for iOS|work=The Next Web|first=Owen|last=Williams|date=June 2, 2014|access-date=June 2, 2014}}</ref> It underwent an upgrade to version 1.2 during 2014 and a major upgrade to Swift 2 at WWDC 2015. Initially a proprietary language, version 2.2 was made [[Open-source software|open-source software]] under the [[Software:Apache License|Apache License]] 2.0 on December 3, 2015, for Apple's platforms and [[Software:Linux|Linux]].<ref>{{Cite web|title = Apple's new programming language Swift is now open source|url = https://www.theverge.com/2015/12/3/9842854/apple-swift-open-source-released|website = The Verge|date = December 3, 2015|access-date = December 5, 2015}}</ref><ref>{{Cite web|title = Apple Open Sources Swift in Latest Pitch to the Enterprise|url = https://blogs.wsj.com/cio/2015/12/03/apple-open-sources-swift-in-latest-pitch-to-the-enterprise/ |work={{wipe|The Wall Street Journal}} Blogs |department=CIO Journal |url-access=registration |date = December 3, 2015|access-date = December 5, 2015}}</ref>

Through version 3.0 the syntax of Swift went through significant evolution, with the core team making source stability a focus in later versions.<ref>{{Cite web|title = Looking back on Swift 3 and ahead to Swift 4|url = https://forums.swift.org/t/looking-back-on-swift-3-and-ahead-to-swift-4/3610|website = Swift Forums|date = July 29, 2016|access-date = November 19, 2018}}</ref><ref>{{Cite web|title = Swift-Evolution|url = https://github.com/apple/swift-evolution#source-stability|website = Swift Evolution|access-date = November 19, 2018}}</ref> In the first quarter of 2018 Swift surpassed [[Objective-C]] in measured popularity.<ref>{{Cite web|url=https://redmonk.com/sogrady/2018/03/07/language-rankings-1-18/|title=The RedMonk Programming Language Rankings: January 2018 – tecosystems|website=redmonk.com|date=March 7, 2018|language=en-US|access-date=2018-11-20}}</ref>

Swift 4.0, released in 2017, introduced several changes to some built-in classes and structures. Code written with previous versions of Swift can be updated using the migration functionality built into Xcode. Swift 5, released in March 2019, introduced a stable binary interface on Apple platforms, allowing the Swift runtime to be incorporated into Apple operating systems. It is source compatible with Swift 4.<ref>{{cite web|url=https://swift.org/blog/swift-5-released/|title=Swift 5 Released!|last=Kremenek|first=Ted|date=March 25, 2019}}</ref>

Swift 5.1 was officially released in September 2019. Swift 5.1 builds on the previous version of Swift 5 by extending the stable features of the language to compile-time with the introduction of module stability. The introduction of module stability makes it possible to create and share binary frameworks that will work with future releases of Swift.<ref>{{cite web|url=https://swift.org/blog/swift-5-1-released/|title=Swift 5.1 Released!|last=Kremenek|first=Ted|date=September 20, 2019|access-date=October 28, 2019|archive-date=February 26, 2022|archive-url=https://web.archive.org/web/20220226203243/https://www.swift.org/blog/swift-5-1-released/|url-status=dead}}</ref>

Swift 5.5, officially announced by Apple at the 2021 WWDC, significantly expands language support for [[Concurrency (computer science)|concurrency]] and [[Asynchrony (computer programming)|asynchronous code]], notably introducing a unique version of the [[Actor model|actor model]].<ref>{{cite web|url=https://www.hackingwithswift.com/articles/233/whats-new-in-swift-5-5|title=What's new in Swift 5.5?|last=Hudson|first=Paul|date=June 6, 2021|website=HackingWithSwift.com|publisher=Hacking with Swift|access-date=2021-06-08}}</ref>

The current version, Swift 5.9, was released in September 2023 and includes a macro system, generic parameter packs, and ownership features like the new <code>consume</code> operator.<ref>{{Cite web |date=2023-09-18 |title=Swift 5.9 Released |url=https://swift.org/blog/swift-5.9-released/ |access-date=2023-10-09 |website=Swift.org |language=en}}</ref>

== History ==

Development of Swift started in July 2010 by [[Biography:Chris Lattner|Chris Lattner]], with the eventual collaboration of many other programmers at [[Company:Apple Inc.|Apple]]. Swift was motivated by the need for a replacement for Apple's earlier programming language [[Objective-C]], which had been largely unchanged since the early 1980s and lacked modern language features. Swift took language ideas "from [[Objective-C]], [[Rust (programming language)|Rust]], [[Haskell (programming language)|Haskell]], [[Ruby (programming language)|Ruby]], [[Python (programming language)|Python]], [[C Sharp (programming language)|C#]], [[CLU (programming language)|CLU]], and far too many others to list".<ref name="lattner 2014 info 1" /> On June 2, 2014, the Apple Worldwide Developers Conference (WWDC) application became the first publicly released app written with Swift.<ref name=stateoftheplatforms /> A [[Software release life cycle#Beta|beta version]] of the [[Programming language|programming language]] was released to registered Apple developers at the conference, but the company did not promise that the final version of Swift would be [[Source code|source code]] compatible with the test version. Apple planned to make source code converters available if needed for the full release.<ref name=stateoftheplatforms>Platforms State of the Union, Session 102, Apple Worldwide Developers Conference, June 2, 2014</ref>

''The Swift Programming Language'', a free 500-page manual, was also released at WWDC, and is available on the [[Software:Apple Books|Apple Books]] Store and the official website.<ref name="Apple swift book">{{cite book|url=https://itunes.apple.com/book/swift-programming-language/id881256329?mt=11|title=The Swift Programming Language|date=June 2, 2014|publisher=[[Company:Apple Inc.|Apple]]|access-date=June 2, 2014}}
*{{cite web |title=Documentation |url=https://swift.org/documentation/ |website=Swift}}</ref>

Swift reached the 1.0 milestone on September 9, 2014, with the ''Gold Master'' of [[Software:Xcode|Xcode]] 6.0 for [[Software:IOS|iOS]].<ref name="Swift Blog">{{cite web|url=https://developer.apple.com/swift/blog/?id=14|title=Swift Has Reached 1.0|date=September 9, 2014|access-date=September 10, 2014}}</ref> Swift 1.1 was released on October 22, 2014, alongside the launch of Xcode 6.1.<ref name="Xcode 6.1 release notes">{{cite web|url=https://developer.apple.com/library/ios/releasenotes/DeveloperTools/RN-Xcode/Chapters/xc6_release_notes.html|title=Xcode 6.1 Release Notes|date=October 22, 2014|access-date=January 23, 2015}}</ref> Swift 1.2 was released on April 8, 2015, along with Xcode 6.3.<ref name="Xcode 6.3 release notes">{{cite web|url=https://developer.apple.com/library/ios/releasenotes/DeveloperTools/RN-Xcode/Chapters/xc6_release_notes.html|title=Xcode 6.3 Release Notes|date=April 8, 2015|access-date=April 8, 2015}}</ref> Swift 2.0 was announced at WWDC 2015, and was made available for publishing apps in the App Store on September 21, 2015.<ref>{{Cite web|url=https://developer.apple.com/swift/blog/?id=32|title=Swift 2 Apps in the App Store |website=Swift Blog|access-date=March 13, 2016}}</ref> Swift 3.0 was released on September 13, 2016.<ref>{{Cite news|url=https://swift.org/blog/swift-3-0-released/|title=Swift 3.0 Released!|date=September 13, 2016|newspaper=Swift.org|access-date=October 26, 2016|archive-date=October 14, 2016|archive-url=https://web.archive.org/web/20161014162805/https://swift.org/blog/swift-3-0-released/|url-status=dead}}</ref> Swift 4.0 was released on September 19, 2017.<ref>{{Cite news|url=https://swift.org/blog/swift-4-0-released/|title=Swift 4.0 Released!|date=September 17, 2017|newspaper=Swift.org|access-date=March 1, 2018|archive-date=March 28, 2019|archive-url=https://web.archive.org/web/20190328104443/https://swift.org/blog/swift-4-0-released/|url-status=dead}}</ref> Swift 4.1 was released on March 29, 2018.<ref>{{Cite news|url=https://swift.org/blog/swift-4-1-released/|title=Swift 4.1 Released!|date=March 29, 2018|newspaper=Swift.org|access-date=March 30, 2018|archive-date=April 25, 2019|archive-url=https://web.archive.org/web/20190425153237/https://swift.org/blog/swift-4-1-released/|url-status=dead}}</ref>

Swift won first place for ''Most Loved Programming Language'' in the [[Stack Overflow]] Developer Survey 2015<ref name="Stack Overflow Developer Survey Results 2015">{{cite web|url=https://stackoverflow.com/research/developer-survey-2015#tech-super|title=Stack Overflow Developer Survey Results 2015}}</ref> and second place in 2016.<ref name="Stack Overflow Developer Survey Results 2016">{{cite web|url=https://stackoverflow.com/research/developer-survey-2016#technology-most-loved-dreaded-and-wanted|title=Stack Overflow Developer Survey Results 2016}}</ref>

On December 3, 2015, the Swift language, supporting libraries, debugger, and package manager were open-sourced under the Apache 2.0 license with a Runtime Library Exception,<ref>{{cite web |title=Swift.org and Open Source |url=https://swift.org/about/#swiftorg-and-open-source |website=Swift.org |publisher=Apple Inc. |access-date=25 February 2019}}</ref> and [https://swift.org Swift.org] was created to host the project. The source code is hosted on [https://github.com/apple/swift GitHub], where it is easy for anyone to get the code, build it themselves, and even create pull requests to contribute code back to the project.

In December 2015, [[Company:IBM|IBM]] announced its Swift Sandbox website, which allows developers to write Swift code in one pane and display output in another.<ref>{{Cite web|url=https://developer.ibm.com/swift/2015/12/03/introducing-the-ibm-swift-sandbox/|title=Introducing the IBM Swift Sandbox&nbsp;— Swift|website=Swift|language=en-US|access-date=December 5, 2015}}</ref><ref>{{Cite web|url=https://9to5mac.com/2015/12/04/swift-web-browser-code-ibm-sandbox/|title=Write Swift code in a web browser with the IBM Swift Sandbox|last=Mayo|first=Benjamin|website=9to5Mac|date=December 4, 2015|access-date=December 5, 2015}}</ref><ref>{{Cite web|url=https://www.zdnet.com/article/after-apple-open-sources-it-ibm-puts-swift-in-the-cloud/|title=After Apple open sources it, IBM puts Swift programming in the cloud {{!}} ZDNet|website=ZDNet|access-date=December 5, 2015}}</ref> The Swift Sandbox was deprecated in January 2018.<ref>{{Cite web|url=https://developer.ibm.com/swift/2017/12/07/package-catalog-sandbox-deprecation/|title=Swift Package Catalog and Swift Sandbox Deprecation|language=en-US|access-date=November 9, 2018}}</ref>

During the WWDC 2016, Apple announced an [[Engineering:IPad|iPad]] exclusive [[Mobile app|app]], named [[Software:Swift Playgrounds|Swift Playgrounds]], intended to teach people how to code in Swift. The app is presented in a 3D video game-like interface which provides feedback when lines of code are placed in a certain order and executed.<ref>{{Cite web|url=https://developer.apple.com/swift/playgrounds/|title=Swift Playgrounds |website=Apple Developer|access-date=June 19, 2016}}</ref><ref>{{Cite web|url=https://www.apple.com/swift/playgrounds/|title=Swift Playgrounds&nbsp;— Preview|website=Apple|language=en-US|access-date=June 19, 2016}}</ref><ref>{{Cite web|url=https://9to5mac.com/2016/06/13/apple-announces-swift-playgrounds-for-ipad/|title=Apple announces Swift Playgrounds for iPad at WWDC, public release in fall|last=Mayo|first=Benjamin|date=June 13, 2016|website=9to5Mac|access-date=June 19, 2016}}</ref>

In January 2017, Chris Lattner announced his departure from Apple for a new position with Tesla Motors, with the Swift project lead role going to team veteran Ted Kremenek.<ref>{{cite web|url=https://arstechnica.com/apple/2017/01/longtime-apple-programmer-and-swift-creator-leaves-apple-for-tesla |title=Longtime Apple programmer and Swift creator leaves Apple for Tesla |first=Andrew |last=Cunningham |date=January 10, 2017 |publisher=Ars Technica}}</ref><ref>{{cite web|url=https://appleinsider.com/articles/17/01/13/new-swift-project-head-ted-kremenek-said-to-be-running-the-show-behind-the-scenes-for-some-time |title=New Swift project head Ted Kremenek said to be running the show behind the scenes for some time |first=Mike |last=Wuerthele |date=January 13, 2017 |publisher=AppleInsider}}</ref>

During WWDC 2019, Apple announced SwiftUI with Xcode 11, which provides a framework for [[Declarative programming|declarative]] UI structure design across all Apple platforms.<ref>{{Cite web|url=https://appleinsider.com/articles/19/06/19/wwdc19-swiftui-was-the-brightest-star-in-a-galaxy-of-new-ideas|title=WWDC19: SwiftUI was the brightest star in a galaxy of new ideas|author=Daniel Eran Dilger|website=AppleInsider|language=en|access-date=2019-07-19}}</ref>

Official downloads for the [[Software:Ubuntu|Ubuntu]] distribution of Linux have been available since Swift 2.2, with more distros added since Swift 5.2.4, [[Software:CentOS|CentOS]] and Amazon Linux.<ref>{{Cite web|url=https://swift.org/download/#releases|title=Swift.org - Download Swift|access-date=2020-06-21}}</ref> There is an unofficial SDK and native toolchain package for Android too.<ref>{{Cite web|url=https://github.com/buttaface/swift-android-sdk|title=Android SDKs for Swift|website=[[GitHub]]|access-date=2021-09-10}}</ref><ref>{{Cite web|url=https://repology.org/project/swift-lang/versions|title=swift-lang package versions|access-date=2021-09-10}}</ref>

=== Platforms ===

The platforms Swift supports are Apple's operating systems ([[Software:Darwin (operating system)|Darwin]], [[Software:IOS|iOS]], [[Software:IPadOS|iPadOS]], [[Software:MacOS|macOS]], [[Software:TvOS|tvOS]], [[Software:WatchOS|watchOS]]), [[Software:Linux|Linux]], [[Software:Windows|Windows]], and [[Software:Android (operating system)|Android]].<ref name="Swift Android Toolchain">{{Cite web|last=Readdle|date=2020-01-15|title=Swift for Android: Our Experience and Tools|url=https://blog.readdle.com/why-we-use-swift-for-android-db449feeacaf|access-date=2020-08-20|website=Medium|language=en}}</ref><ref name="Swift for Windows">{{cite web |last=Anderson |first=Tim |date=March 30, 2020 |title=Official tailored Swift for Windows support promised in 5.3: Swift on more platforms – provided you do not need a GUI |url=https://www.theregister.com/2020/03/30/official_swift_programming_for_windows/ |website=The Register |access-date=2020-09-18}}</ref>

A key aspect of Swift's design is its ability to interoperate with the huge body of existing Objective-C code developed for Apple products over the previous decades, such as Cocoa and the Cocoa Touch [[Software framework|frameworks]]. On Apple platforms,<ref>{{cite web |date=December 3, 2015 |title=The Swift Linux Port |url=https://swift.org/blog/swift-linux-port/ |access-date=August 3, 2016 |website=Swift.org |publisher=Apple Inc |language=en-US}}</ref> it links with the Objective-C [[Runtime library|runtime library]], which allows [[C (programming language)|C]], [[Objective-C]], [[C++]] and Swift code to run within one program.<ref>{{cite web|last1=Timmer|first1=John|title=A fast look at Swift, Apple's new programming language|url=https://arstechnica.com/apple/2014/06/a-fast-look-at-swift-apples-new-programming-language/|website=[[Ars Technica]]|publisher=Condé Nast|access-date=June 6, 2014|date=June 5, 2014}}</ref>

=== Version history ===
{| class = "wikitable sortable" style="font-size: 85%; width: auto;"
|-
! Version
! Release Date
! [[Software:MacOS|macOS]]
! [[Software:Linux|Linux]]
! [[Software:Windows|Windows]]
|-
| Swift 1.0
| September 9, 2014
| {{yes}}
| {{no}}
| {{no}}
|-
| Swift 1.1
| October 22, 2014
| {{yes}}
| {{no}}
| {{no}}
|-
| Swift 1.2
| April 8, 2015
| {{yes}}
| {{no}}
| {{no}}
|-
| Swift 2.0
| September 21, 2015
| {{yes}}
| {{no}}
| {{no}}
|-
| Swift 2.1
| October 20, 2015
| {{yes}}
| {{no}}
| {{no}}
|-
| Swift 2.2
| March 21, 2016
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 2.2.1
| May 3, 2016
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 3.0
| September 13, 2016
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 3.0.1
| October 28, 2016
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 3.0.2
| December 13, 2016
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 3.1
| March 27, 2017
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 3.1.1
| April 21, 2017
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.0
| September 19, 2017
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.0.2
| November 1, 2017
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.0.3
| December 5, 2017
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.1
| March 29, 2018
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.1.1
| May 4, 2018
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 4.1.2
| May 31, 2018
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.1.3
| July 27, 2018
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 4.2
| September 17, 2018
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.2.1
| October 30, 2018
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 4.2.2
| February 4, 2019
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 4.2.3
| February 28, 2019
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 4.2.4
| March 29, 2019
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.0<ref>{{Cite web|url=https://swift.org/blog/swift-5-released/|title=Swift 5 Released!|last=Kremenek|first=Ted|date=2019-03-25|website=Swift.org|language=en|access-date=2019-03-28}}</ref>
| March 25, 2019
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.0.1
| April 18, 2019
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.0.2
| July 15, 2019
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.0.3
| August 30, 2019
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.1
| September 10, 2019
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.1.1
| October 11, 2019
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.1.2
| November 7, 2019
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.1.3
| December 13, 2019
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.1.4
| January 31, 2020
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.1.5
| March 9, 2020
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.2
| March 24, 2020
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.2.1
| March 30, 2020
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.2.2
| April 15, 2020
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.2.3
| April 29, 2020
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.2.4
| May 20, 2020
| {{yes}}
| {{yes}}
| {{no}}
|-
| Swift 5.2.5
| August 5, 2020
| {{no}}
| {{yes}}
| {{no}}
|-
| Swift 5.3
| September 16, 2020
| {{yes}}
| {{yes}}
| {{yes}}<ref>{{cite web |title=Download Swift |url=https://swift.org/download/#releases |website=Swift.org |publisher=Apple |access-date=15 December 2020}}</ref>
|-
| Swift 5.3.1
| November 13, 2020
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.3.2
| December 15, 2020
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.3.3
| January 25, 2021
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.4<ref>{{cite web |last1=Kremenek |first1=Ted |title=Swift 5.4 Released! |url=https://swift.org/blog/swift-5-4-released/ |website=Swift.org |access-date=26 April 2021 |language=en |date=26 April 2021 |publisher=Apple |archive-date=April 26, 2021 |archive-url=https://web.archive.org/web/20210426183534/https://swift.org/blog/swift-5-4-released/ |url-status=dead }}</ref>
| April 26, 2021
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.4.1
| May 25, 2021
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.4.2
| June 28, 2021
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.4.3
| September 9, 2021
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.5
| September 20, 2021
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.5.1
| October 27, 2021
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.5.2
| December 14, 2021
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.5.3
| February 9, 2022
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.6<ref>{{cite web |last1=Kremenek |first1=Ted |title=Swift 5.6 Released! |url=https://www.swift.org/blog/swift-5.6-released/ |website=Swift.org |access-date=14 March 2022 |language=en |date=14 March 2022 |publisher=Apple}}</ref>
| March 14, 2022
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.6.1<ref>{{Cite web | url=https://github.com/apple/swift/releases/tag/swift-5.6.1-RELEASE | title=Release Swift 5.6.1 Release · apple/Swift | website=[[GitHub]] }}</ref>
| April 9, 2022
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.6.2<ref>{{Cite web | url=https://github.com/apple/swift/releases/tag/swift-5.6.2-RELEASE | title=Release Swift 5.6.2 Release · apple/Swift | website=[[GitHub]] }}</ref>
| June 15, 2022
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.6.3<ref>{{Cite web | url=https://github.com/apple/swift/releases/tag/swift-5.6.3-RELEASE | title=Release Swift 5.6.3 Release · apple/Swift | website=[[GitHub]] }}</ref>
| September 2, 2022
| {{no}}
| {{yes}}
| {{yes}}
|-
| Swift 5.7<ref>{{cite web |last1=Borla |first1=Holly |title=Swift 5.7 Released! |url=https://www.swift.org/blog/swift-5.7-released/ |website=Swift.org |access-date=23 September 2022 |language=en |date=12 September 2022 |publisher=Apple}}</ref>
| September 12, 2022
| {{yes}}
| {{yes}}
| {{yes}}
|-
| Swift 5.7.1<ref>{{Cite web | url=https://github.com/apple/swift/releases/tag/swift-5.7.1-RELEASE | title=Release Swift 5.7.1 Release · apple/Swift | website=[[GitHub]] }}</ref>
| November 1, 2022
| {{yes}}
| {{yes}}
| {{yes}}
|-
|Swift 5.8<ref>{{Cite web | url=https://github.com/apple/swift/releases/tag/swift-5.8-RELEASE | title=Release Swift 5.8 Release · apple/Swift | website=[[GitHub]] }}</ref>
|March 30, 2023
|{{yes}}
|{{yes}}
|{{yes}}
|-
|Swift 5.8.1<ref>{{Cite web |title=Release Swift 5.8.1 Release · apple/swift |url=https://github.com/apple/swift/releases/tag/swift-5.8.1-RELEASE |access-date=2023-06-14 |website=GitHub |language=en}}</ref>
|June 1, 2023|June 1, 2023
|{{yes}}
|{{yes}}
|{{yes}}
|-
|Swift 5.9<ref>{{Cite web |title=Release Swift 5.9 Release · apple/swift |url=https://github.com/apple/swift/releases/tag/swift-5.9-RELEASE |access-date=2023-09-18 |website=GitHub |language=en}}</ref>
|September 18, 2023|September 18, 2023
|{{yes}}
|{{yes}}
|{{yes}}
|-
|Swift 5.9.1<ref>{{Cite web |title=Release Swift 5.9.1 Release · apple/swift |url=https://github.com/apple/swift/releases/tag/swift-5.9.1-RELEASE |access-date=2023-10-19 |website=GitHub |language=en}}</ref>
|October 19, 2023|October 19, 2023
|{{yes}}
|{{yes}}
|{{yes}}
|-
|Swift 5.9.2<ref>{{Cite web |title=Release Swift 5.9.2 Release · apple/swift |url=https://github.com/apple/swift/releases/tag/swift-5.9.2-RELEASE |access-date=2023-12-11 |website=GitHub |language=en}}</ref>
|December 11, 2023|December 11, 2023
|{{yes}}
|{{yes}}
|{{yes}}
|}

== Features ==

Swift is general purpose programming language that employs modern programming-language theory concepts and strives to present a simple, yet powerful syntax. Swift incorporates innovations and conventions from various programming languages, with notable inspiration from Objective-C, which it replaced as the primary development language on Apple Platforms.

Swift was designed to be safe and friendly to new programmers while not sacrificing speed. By default Swift manages all memory automatically and ensures variables are always initialized before use. Array accesses are checked for out-of-bounds errors and integer operations are checked for overflow. Parameter names allow for the creation of clear APIs. Protocols define interfaces that types may adopt, while extensions allow developers to add functionality to existing types. Swift enables [[Object-oriented programming|Object-Oriented Programming]] with the support for [[Class (computer programming)|classes]], [[Subtyping|subtyping]], and method overriding. Optionals allow [[Null pointer|nil]] values to be handled explicitly and safely. Concurrent programs can be written using async/await syntax and [[Actor model|actors]] isolate shared mutable state in order to eliminate data races.<ref>{{cite web |title=Documentation |url=https://docs.swift.org/swift-book/documentation/the-swift-programming-language/aboutswift |access-date=17 November 2023 |website=docs.swift.org}}</ref><ref name="Eliminate data races using Swift Concurrency">{{cite web |url=https://developer.apple.com/wwdc22/110351 |access-date=17 November 2023 |publisher=Apple Inc |title=Eliminate data races using Swift Concurrency - WWDC22 - Videos }}</ref>

=== Basic Syntax ===
Swift's syntax is similar to C-style languages. Code begins executing in the global scope by default.<ref name="Documentation">{{Cite web |title=Documentation |url=https://docs.swift.org/swift-book/documentation/the-swift-programming-language/guidedtour/ |access-date=2023-10-15 |website=docs.swift.org}}</ref> Alternatively, the {{code|@main|swift}} attribute can be applied a structure, class, or enumeration declaration to indicate that it contains the program's entry point.<ref>{{Cite web |title=Documentation |url=https://docs.swift.org/swift-book/documentation/the-swift-programming-language/attributes/#main |access-date=2023-10-15 |website=docs.swift.org}}</ref>

Swift's "Hello, World!" program is:<source lang="swift" line="1" start="1">print("Hello, world!")
</source>The {{code|print(_:separator:terminator:)|swift}} function used here is included in Swift's standard library, which is available to all programs without the need to import external modules. Statements in Swift don't have to end with a semicolon, however semicolons are required to separate multiple statements written on the same line. Single-line [[Comment (computer programming)|comments]] begin with {{code|//|swift}} and continue until the end of the current line. Multiline comments are contained by {{code|/*|swift}} and {{code|*/|swift}} characters.

Constants are declared with the {{code|let|swift}} keyword and variables with the {{code|var
|swift}} keyword. Values must be initialized before they are read. Values may infer their type based on the type of the provided initial value. If the initial value is set after the value's declaration, a type must be declared explicitly.<ref name="Documentation"/><source lang="swift" line="1" start="1">let highScoreThreshold = 1000 // A constant with type Int. The type was inferred based on the provided value.

var currentScore = 980 // A variable with type Int.
currentScore = 1200 // The value of variables can change over time.

let playerMessage: String // A constant with explicit type String.
if currentScore > highScoreThreshold {
    playerMessage = "You are a top player!"
} else {
    playerMessage = "Better luck next time."
}

print(playerMessage) // Prints "You are a top player!"
</source>Control flow in Swift is managed with if-else, guard, and [[Switch statement|switch]] statements, along with [[While loop|while]] and [[For loop|for-in loops]].

If statements take a boolean parameter and execute the body of the if statement if the condition is true, otherwise it executes the optional {{code|else|swift}} body. {{code|if-let|swift}} syntax provides syntactic sugar for checking for the existence of an optional value and unwrapping it at the same time.<source lang="swift" line="1" start="1">let someNumber = 42
if someNumber % 2 == 0 { // Use the remainder operator to find the remainder of someNumber divided by 2.
    print("\(someNumber) is even.")
} else{
   print("\(someNumber) is odd.")
}

// Prints "42 is even."
</source>Functions are defined with the <code>{{code|func|swift}}</code> keyword. Functions parameters may have names which allow function calls to read like phrases. An underscore before the parameter name allows the argument label to be omitted from the call site. [[Tuple]]s can be used functions to return multiple pieces of data at once.<source lang="swift" line="1" start="1">func constructGreeting(for name: String) -> String {
    return "Hello \(name)!"
}

let greeting = constructGreeting(for: "Craig")

print(greeting) // Prints "Hello Craig!"
</source>Functions, and anonymous functions known as [[Closure (computer programming)|closures]], can be assigned to properties and passed around the program like any other value.<source lang="swift" line="1" start="1">func divideByTwo(_ aNum: Int) -> Int {
    return aNum / 2
}

func multiplyByTwo(_ aNum: Int) -> Int {
    return aNum * 2
}

let mathOperation = multiplyByTwo

print(mathOperation(21)) // Prints "42"
</source><code>{{code|guard|swift}}</code> statements require that the given condition is true before continuing on past the <code>{{code|guard|swift}}</code> statement, otherwise the body of the provided <code>{{code|else|swift}}</code> clause is run. The <code>{{code|else|swift}}</code> clause must exit control of the code block in which the <code>{{code|guard|swift}}</code> statement appears. <code>{{code|guard|swift}}</code> statements are useful for ensuring that certain requirements are met before continuing on with program execution. In particular they can be used to create an unwrapped version of an optional value that is guaranteed to be non-nil for the remainder of the enclosing scope.<source lang="swift" line="1" start="1">func divide(numerator: Int?, byDenominator denominator: Int) -> Int? {
    guard denominator != 0 else {
        print("Can't divide by 0.")
        return nil
    }
    
    guard let numerator else {
        print("The provided numerator is nil.")
        return nil
    }
    
    return numerator / denominator
}

let result = divide(numerator: 3, byDenominator: 0)
print("Division result is: \(result)")

// Prints:
// "Can't divide by 0."
// "Division result is: nil."
</source><code>[[Switch statement|switch]]</code> statements compare a value with multiple potential values and then executes an associated code block. <code>switch</code> statements must be made exhaustive, either by including cases for all possible values or by including a <code>default</code> case which is run when the provided value doesn't match any of the other cases. <code>switch</code> cases do not implicitly fall through, although they may explicitly do so with the <code>fallthrough</code> keyword. [[Pattern matching]] can be used in various ways inside <code>switch</code> statements. Here is an example of an integer being matched against a number of potential ranges:<source lang="swift" line="1" start="1">let someNumber = 42

switch someNumber {
case ..<0: 
    print("\(someNumber) negative.")
case 0: 
    print("\(someNumber) is 0.")
case 1...9:
    print("\(someNumber) greater than 0, but less than 10.")
default: 
    print("\(someNumber) is greater than 9.")
}

// Prints "42 is greater than 9."
</source><code>for-in</code> loops iterate over a sequence of values:<source lang="swift" line="1" start="1">let names = ["Will", "Anna", "Bart"]
for name in names {
    print(name)
}
// Prints:
// Will
// Anna
// Bart
</source><code>[[While loop|while]]</code> loops iterate as long as the given boolean condition evaluates to <code>true</code>:<source lang="swift" line="1" start="1">// Add together all the numbers from 1 to 5.
var i = 1
var result = 0

while i <= 5 { // The loop performs its body as long as i is less than or equal to 5.  
    result += i // Add i to the current result.
    i += 1 // Increment i by 1.
}

print(result) // Prints "15"

</source>

=== Closure support ===
Swift supports [[Closure (computer programming)|closures]], which are self-contained blocks of functionality that can be passed around and used in code,<ref>{{Cite web|title=Closures — The Swift Programming Language (Swift 5.5)|url=https://docs.swift.org/swift-book/LanguageGuide/Closures.html|access-date=2021-08-31|website=docs.swift.org}}</ref> and can also be used as [[Anonymous function|anonymous function]]s. Here are some examples:

<source lang="swift" line="1" start="1">// Closure type, defined by its input and output values, can be specified outside the closure:
let closure1: (Int, Int) -> Int = { arg1, arg2 in
    return arg1 + arg2
}

// …or inside it:
let closure2 = { (arg1: Int, arg2: Int) -> Int in
    return arg1 + arg2
}

// In most cases, closure's return type can be inferred automatically by the compiler.
let closure3 = { arg1: Int, arg2: Int in
    return arg1 + arg2
}
</source>
Closures can be assigned to variables and constants, and can be passed into other functions or closures as parameters. Single-expression closures may drop the {{code|return|swift}} keyword.

Swift also has a trailing closure syntax, which allows the closure to be written after the end of the function call instead of within the function's parameter list. Parentheses can be omitted altogether if the closure is the function's only parameter:
<source lang="swift" line="1" start="1">// This function takes a closure which receives no input parameters and returns an integer,
// evaluates it, and uses the closure's return value (an Int) as the function's return value.
func foo(closure bar: () -> Int) -> Int {
    return bar()
}

// Without trailing closure syntax:
foo(closure: { return 1 })

// With trailing closure syntax, and implicit return:
foo { 1 } </source>

Starting from version 5.3, Swift supports multiple trailing closures:<ref>{{cite web |last1=Macomber |first1=Kyle |last2=Yaskevich |first2=Yavel |last3=Gregor |first3=Doug |last4=McCall |first4=John |title=Multiple Trailing Closures |url=https://github.com/apple/swift-evolution/blob/b394ae8fff585c8fdc27a50422ea8a90f13138d2/proposals/0279-multiple-trailing-closures.md |website=GitHub |access-date=19 October 2020}}</ref>

<source lang="swift">
// This function passes the return of the first closure as the parameter of the second,
// and returns the second closure's result:
func foo(bar: () -> Int, baz: (Int) -> Int) -> Int {
    return baz(bar())
}

// With no trailing closures:
foo(bar: { return 1 }, baz: { x in return x + 1 })

// With 1 trailing closure:
foo(bar: { return 1 }) { x in return x + 1 }

// With 2 trailing closures (note that only the first closure's argument name is omitted):
foo { return 1 } baz: { x in return x + 1 }
</source>Swift will provide shorthand argument names for inline closures, removing the need to explicitly name all of the closures parameters.<ref>{{Cite web |title=Documentation |url=https://docs.swift.org/swift-book/documentation/the-swift-programming-language/closures/ |access-date=2023-10-16 |website=docs.swift.org}}</ref> Arguments can be referred to with the names $0, $1, $2, and so on:<source lang="swift">
let names = ["Josephine", "Steve", "Chris", "Barbara"]

// filter calls the given closure for each value in names. 
// Values with a character count less than 6 are kept, the others are dropped.
let shortNames = names.filter { $0.count < 6 }

print(shortNames) // Prints "["Steve", "Chris"]"
</source>Closures may capture values from their surrounding scope. The closure will refer to this captured value for as long as the closure exists:<source lang="swift">
func makeMultiplier(withMultiple multiple: Int) -> (Int) -> (Int) {
    // Create and return a closure that takes in an Int and returns the input multiplied by the value of multiple.
    return {
        $0 * multiple
    }
}

let multiplier = makeMultiplier(withMultiple: 3)
print(multiplier(3)) // Prints "9"
print(multiplier(10)) // Prints "30"
</source>

=== String support ===
The Swift standard library includes unicode-compliant {{code|String|swift}} and {{code|Character|swift}} types. String values can be initialized with a String literal, a sequence of characters surrounded by double quotation marks. Strings can be concatenated with the {{code|+|swift}} operator:

<source lang="swift">var someString = "Hello,"
someString += " world!"</source>String interpolation allows for the creation of a new string from other values and expressions. Values written between parentheses preceded by a {{code|\|swift}} will be inserted into the enclosing string literal:<ref>{{Cite web |title=Strings and Characters |url=https://docs.swift.org/swift-book/documentation/the-swift-programming-language/stringsandcharacters/ |access-date=2023-10-16 |website=docs.swift.org}}</ref>

<source lang="swift">var currentScore = 980
print("Your score is \(currentScore).")

// Prints "Your score is 980."</source>A for-in loop can be used to iterate over the characters contained in a string:

<source lang="swift">for character in "Swift" {
    print(character)
}
// S
// w
// i
// f
// t</source>When the Foundation framework is imported Swift invisibly bridges the String type to NSString, the String class commonly used in Objective-C.

=== Callable objects ===
{{excerpt|Callable object|In Swift}}

=== Access control ===
Swift supports five access control levels for symbols: {{code|open|swift}}, {{code|public|swift}}, {{code|internal|swift}}, {{code|fileprivate|swift}}, and {{code|private|swift}}. Unlike many object-oriented languages, these access controls ignore [[Inheritance (object-oriented programming)|inheritance]] hierarchies: {{code|private|swift}} indicates that a symbol is accessible only in the immediate scope, {{code|fileprivate|swift}} indicates it is accessible only from within the file, {{code|internal|swift}} indicates it is accessible within the containing module, {{code|public|swift}} indicates it is accessible from any module, and {{code|open|swift}} (only for classes and their methods) indicates that the class may be subclassed outside of the module.<ref>{{cite web|title=Access Control|url=https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AccessControl.html|website=developer.apple.com|publisher=[[Company:Apple Inc.|Apple Inc.]]|access-date=October 25, 2016}}</ref>

=== Optionals and chaining ===
An important feature in Swift is [[Option type|option type]]s, which allow [[Reference (computer science)|references]] or values to operate in a manner similar to the common pattern in [[C (programming language)|C]], where a [[Pointer (computer programming)|pointer]] may either refer to a specific value or no value at all. This implies that non-optional types cannot result in a [[Pointer (computer programming)#Making pointers safer|null-pointer error]]; the compiler can ensure this is not possible.

Optional types are created with the <code>Optional</code> enum. To make an Integer that is nullable, one would use a declaration similar to <code>var optionalInteger: Optional<Int></code>. As in C#,<ref>[https://msdn.microsoft.com/en-us/library/1t3y8s4s.aspx "Nullable Types"], C# Programming Guide, Microsoft.</ref> Swift also includes syntactic sugar for this, allowing one to indicate a variable is optional by placing a question mark after the type name, <code>var optionalInteger: Int?</code>.<ref>{{cite web |title=Types |url=https://developer.apple.com/library/prerelease/ios/documentation/swift/conceptual/swift_programming_language/Types.html |website=developer.apple.com |publisher=[[Company:Apple Inc.|Apple Inc.]] |access-date=July 16, 2014}}</ref> Variables or constants that are marked optional either have a value of the underlying type or are <code>nil</code>. Optional types ''wrap'' the base type, resulting in a different instance. <code>String</code> and <code>String?</code> are fundamentally different types, the former is of type <code>String</code> while the latter is an <code>Optional</code> that may be holding some <code>String</code> value.

To access the value inside, assuming it is not nil, it must be ''unwrapped'' to expose the instance inside. This is performed with the <code>!</code> operator:

<source lang="swift">
let myValue = anOptionalInstance!.someMethod()
</source>

In this case, the <code>!</code> operator unwraps <code>anOptionalInstance</code> to expose the instance inside, allowing the method call to be made on it. If <code>anOptionalInstance</code> is nil, a null-pointer error occurs, terminating the program. This is known as force unwrapping. Optionals may be safely unwrapped using [[Safe navigation operator|optional chaining]] which first tests whether the instance is nil, and then unwrap it if it is non-null:

<source lang="swift">
let myValue = anOptionalInstance?.someMethod()
</source>

In this case the runtime calls <code>someMethod</code> only if <code>anOptionalInstance</code> is not nil, suppressing the error. A <code>?</code> must be placed after every optional property. If any of these properties are nil the entire expression evaluates as nil. The origin of the term ''chaining'' comes from the more common case where several method calls/getters are chained together. For instance:

<source lang="swift">
let aTenant = aBuilding.tenantList[5]
let theirLease = aTenant.leaseDetails
let leaseStart = theirLease?.startDate
</source>

can be reduced to:

<source lang="swift">
let leaseStart = aBuilding.tenantList[5].leaseDetails?.startDate
</source>

Swift's use of optionals allows the compiler to use [[Static dispatch|static dispatch]] because the unwrapping action is called on a defined instance (the wrapper), versus occurring in a runtime dispatch system.

=== Value types ===
In many object-oriented languages, objects are represented internally in two parts. The object is stored as a block of data placed on the [[Heap (data structure)|heap]], while the name (or "handle") to that object is represented by a [[Pointer (computer programming)|pointer]]. Objects are passed between methods by copying the value of the pointer, allowing the same underlying data on the heap to be accessed by anyone with a copy. In contrast, basic types like integers and floating-point values are represented directly; the handle contains the data, not a pointer to it, and that data is passed directly to methods by copying. These styles of access are termed ''pass-by-reference'' in the case of objects, and ''pass-by-value'' for basic types.

Both concepts have their advantages and disadvantages. Objects are useful when the data is large, like the description of a window or the contents of a document. In these cases, access to that data is provided by copying a 32- or 64-bit value, versus copying an entire data structure. However, smaller values like integers are the same size as pointers (typically both are one [[Word (computer architecture)|word]]), so there is no advantage to passing a pointer, versus passing the value.

Swift offers built-in support for objects using either pass-by-reference or pass-by-value semantics, the former using the <code>class</code> declaration and the latter using <code>struct</code>. Structs in Swift have almost all the same features as classes: methods, implementing protocols and using the extension mechanisms. For this reason, Apple terms all data generically as ''instances'', versus objects or values. Structs do not support inheritance, however.<ref name=classesstructs>{{cite web |url=https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/ClassesAndStructures.html |title= Classes and Structures |website=Apple.com}}</ref>

The programmer is free to choose which semantics are more appropriate for each data structure in the application. Larger structures like windows would be defined as classes, allowing them to be passed around as pointers. Smaller structures, like a 2D point, can be defined as structs, which will be pass-by-value and allow direct access to their internal data with no indirection or reference counting. The performance improvement inherent to the pass-by-value concept is such that Swift uses these types for almost all common data types, including <code>Int</code> and <code>Double</code>, and types normally represented by objects, like <code>String</code> and <code>Array</code>.<ref name=classesstructs/> Using value types can result in significant performance improvements in user applications as well.<ref>{{cite web |url=https://medium.com/@fielgood/swift-1-1-swift-1-2-and-objective-c-a-performance-case-study-d86f7a333e2a |title=Performance Case Study on Swift 1.1, Swift 1.2, and Objective-C |first=Fiel |last=Guhit|date=February 14, 2015 }}</ref>

<code>Array</code>, <code>Dictionary</code>, and <code>Set</code> all utilize copy on write so that their data are copied only if and when the program attempts to change a value in them. This means that the various accessors have what is in effect a pointer to the same data storage. So while the data is physically stored as one instance in memory, at the level of the application, these values are separate and physical separation is enforced by copy on write only if needed.<ref>{{cite AV media |url=https://developer.apple.com/videos/wwdc/2015/?id=414 |title=Building Better Apps with Value Types |publisher=Apple}}</ref>

=== Extensions ===
Extensions add new functionality to an existing type, without the need to subclass or even have access to the original source code. Extensions can add new methods, initializers, computed properties, subscripts, and protocol conformances.<ref>{{Cite web |title=Documentation |url=https://docs.swift.org/swift-book/documentation/the-swift-programming-language/extensions/ |access-date=2023-11-28 |website=docs.swift.org}}</ref> An example might be to add a spell checker to the base <code>String</code> type, which means all instances of  <code>String</code> in the program gain the ability to spell-check. The system is also widely used as an organizational technique, allowing related code to be gathered into library-like extensions.

Extensions are declared with the <code>extension</code> keyword.<source lang="swift" line="1">
struct Rectangle {
    let width: Double
    let height: Double
}

extension Rectangle {
    var area: Double {
        return height * width
    }
}
</source>

=== Protocol-oriented programming ===
Protocols promise that a particular type implements a set of methods or properties, meaning that other instances in the system can call those methods on any instance implementing that protocol. This is often used in modern object-oriented languages as a substitute for [[Multiple inheritance|multiple inheritance]], although the feature sets are not entirely similar.

In Objective-C, and most other languages implementing the protocol concept, it is up to the programmer to ensure that the required methods are implemented in each class.<ref>{{cite web |url=https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithProtocols/WorkingwithProtocols.html |title=Working with Protocols |website=Apple}}</ref> Swift adds the ability to add these methods using extensions, and to use [[Generic programming|generic programming]] (generics) to implement them. Combined, these allow protocols to be written once and support a wide variety of instances. Also, the extension mechanism can be used to add protocol conformance to an object that does not list that protocol in its definition.<ref name="protocols">{{cite web |title=NSCopying Protocol Reference |url=https://developer.apple.com/library/prerelease/ios/documentation/Cocoa/Reference/Foundation/Protocols/NSCopying_Protocol/index.html |website=Apple}}</ref>

For example, a protocol might be declared called <code>Printable</code>, which ensures that instances that conform to the protocol implement a <code>description</code> property and a <code>printDetails()</code> method requirement:
<source lang="swift">
// Define a protocol named Printable
protocol Printable {
    var description: String { get } // A read-only property requirement
    func printDetails() // A method requirement
}
</source>
This protocol can now be adopted by other types:
<source lang="swift">
// Adopt the Printable protocol in a class
class MyClass: Printable {
    var description: String {
        return "An instance of MyClass"
    }

    func printDetails() {
        print(description)
    }
}
</source>

Extensions can be used to add protocol conformance to types. Protocols themselves can also be extended to provide default implementations of their requirements. Adopters may define their own implementations, or they may use the default implementation:<source lang="swift">
extension Printable { // All Printable instances will receive this implementation, or they may define their own.
    func printDetails() {
        print(description)
    }
}

// Bool now conforms to Printable, and inherits the printDetails() implementation above.
extension Bool: Printable {
    var description: String {
        return "An instance of Bool with value: \(self)"
    }

}
</source>

In Swift, like many modern languages supporting interfaces, protocols can be used as types, which means variables and methods can be defined by protocol instead of their specific type:

<source lang="swift">
func getSomethingPrintable() -> any Printable {
    return true
}

var someSortOfPrintableInstance = getSomethingPrintable()
print(someSortOfPrintableInstance.description)

// Prints "An instance of Bool with value: true"
</source>

It does not matter what concrete type of <code>someSortOfPrintableInstance</code> is, the compiler will ensure that it conforms to the protocol and thus this code is safe. This syntax also means that collections can be based on protocols also, like <code>let printableArray = [any Printable]</code>.

Both extensions and protocols are used extensively in Swift's standard library; in Swift 5.9, approximately 1.2 percent of all symbols within the standard library were protocols, and another 12.3 percent were protocol requirements or default implementations.<ref name="Swift standard library statistics">{{cite web |title=Swift standard library statistics |url=https://swiftinit.org/stats/swift/swift#ss:interface-breakdown |website=swiftinit.org |publisher=Swiftinit |access-date=2 October 2023}}</ref> For instance, Swift uses extensions to add the <code>Equatable</code> protocol to many of their basic types, like Strings and Arrays, allowing them to be compared with the <code>==</code> operator. The <code>Equatable</code> protocol also defines this default implementation:
<source lang="Swift">
func !=<T : Equatable>(lhs: T, rhs: T) -> Bool
</source>
This function defines a method that works on any instance conforming to <code>Equatable</code>, providing a ''not equals'' operator. Any instance, class or struct, automatically gains this implementation simply by conforming to <code>Equatable</code>.<ref>{{cite web |url=https://nshipster.com/swift-default-protocol-implementations/ |title=Swift Default Protocol Implementations |website=NSHipster |first=Mattt |last=Thompson |date=September 2, 2014}}</ref>

Protocols, extensions, and generics can be combined to create sophisticated APIs. For example, constraints allow types to conditionally adopt protocols or methods based on the characteristics of the adopting type. A common use case may be adding a method on collection types only when the elements contained within the collection are <code>Equatable</code>:<source lang="swift">
extension Array where Element: Equatable {

    // allEqual will be available only on instances of Array that contain Equatable elements. 
    func allEqual() -> Bool {
        for element in self {
            if element != self.first {
                return false
            }
        }
        return true
    }
}
</source>

=== Concurrency ===
Swift 5.5 introduced structured concurrency into the language.<ref>{{Cite web |title=swift-evolution/proposals/0304-structured-concurrency.md at main · apple/swift-evolution |url=https://github.com/apple/swift-evolution/blob/main/proposals/0304-structured-concurrency.md |access-date=2023-10-16 |website=GitHub |language=en}}</ref> Structured concurrency uses Async/await syntax similar to Kotlin, JavaScript, and Rust. An async function is defined with the <code>async</code> keyword after the parameter list. When calling an async function the <code>await</code> keyword must be written before the function to indicate that execution will potentially suspend while calling function. While a function is suspended the program may run some other concurrent function in the same program. This syntax allows programs to clearly call out potential suspension points and avoid a version of the [[Pyramid of doom (programming)]] caused by the previously widespread use of closure callbacks.<ref>{{Cite web |title=swift-evolution/proposals/0296-async-await.md at main · apple/swift-evolution |url=https://github.com/apple/swift-evolution/blob/main/proposals/0296-async-await.md#motivation-completion-handlers-are-suboptimal |access-date=2023-10-16 |website=GitHub |language=en}}</ref> <source lang="swift">
func downloadText(name: String) async -> String {
    let result = // ... some asynchronous downloading code ...
    return result
}

let text = await downloadText("text1")
</source>The <code>async let</code> syntax allows multiple functions to run in parallel. <code>await</code> is again used to mark the point at which the program will suspend to wait for the completion of the <code>async</code> functions called earlier.<source lang="swift">
// Each of these calls to downloadText will run in parallel.
async let text1 = downloadText(name: "text1")
async let text2 = downloadText(name: "text2")
async let text3 = downloadText(name: "text3")

let textToPrint = await [text1, text2, text3] // Suspends until all three downloadText calls have returned.
print(textToPrint)
</source>Tasks and TaskGroups can be created explicitly to create a dynamic number of child tasks during runtime:<source lang="swift">
let taskHandle = Task {
    await downloadText(name: "someText")
}

let result = await taskHandle.value
</source>Swift uses the [[Actor model]] to isolate mutable state, allowing different tasks to mutate shared state in a safe manner. Actors are declared with the <code>actor</code> keyword and are reference types, like classes. Only one task may access the mutable state of an actor at the same time. Actors may access and mutate their own internal state freely, but code running in separate tasks must mark each access with the <code>await</code> keyword to indicate that the code may suspend until other tasks finish accessing the actor's state.<source lang="swift">
actor Directory {
    var names: [String] = []
    
    func add(name: String) {
        names.append(name)
    }
}

let directory = Directory()

// Code suspends until other tasks finish accessing the actor.
await directory.add(name: "Tucker")
print(await directory.names)
</source>

=== Libraries, runtime and development ===
On Apple systems, Swift uses the same runtime as the extant [[Objective-C]] system, but requires iOS 7 or macOS 10.9 or higher. It also depends on [[Software:Grand Central Dispatch|Grand Central Dispatch]].<ref>[https://stackoverflow.com/questions/24001778/do-swift-based-apps-work-on-os-x-10-9-ios-7-and-lower/24038997#24038997 "Do Swift-based apps work on macOS 10.9/iOS 7 and lower?"], StackOverflow</ref> Swift and Objective-C code can be used in one program, and by extension, C and C++ also. Beginning in Swift 5.9, [[C++]] code can be used directly from Swift code.<ref>{{Cite web |last=Inc |first=Apple |date=2023-09-18 |title=Swift 5.9 Released |url=https://swift.org/blog/swift-5.9-released/ |access-date=2023-10-09 |website=Swift.org |language=en}}</ref> In the case of Objective-C, Swift has considerable access to the object model, and can be used to subclass, extend and use Objective-C code to provide protocol support.<ref>[https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/WritingSwiftClassesWithObjective-CBehavior.html "Writing Swift Classes with Objective-C Behavior"], Apple Inc.</ref> The converse is not true: a Swift class cannot be subclassed in Objective-C.<ref>{{cite web|url=https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/Migration.html|title=Migrating Your Objective-C Code to Swift}}</ref>

To aid development of such programs, and the re-use of extant code, Xcode 6 and higher offers a semi-automated system that builds and maintains a ''bridging header'' to expose Objective-C code to Swift. This takes the form of an additional header file that simply defines or imports all of the Objective-C symbols that are needed by the project's Swift code. At that point, Swift can refer to the types, functions, and variables declared in those imports as though they were written in Swift. Objective-C code can also use Swift code directly, by importing an automatically maintained header file with Objective-C declarations of the project's Swift symbols. For instance, an Objective-C file in a mixed project called "MyApp" could access Swift classes or functions with the code <code>#import "MyApp-Swift.h"</code>. Not all symbols are available through this mechanism, however—use of Swift-specific features like generic types, non-object optional types, sophisticated enums, or even Unicode identifiers may render a symbol inaccessible from Objective-C.<ref>[https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/MixandMatch.html#//apple_ref/doc/uid/TP40014216-CH10-XID_77 "Swift and Objective-C in the Same Project"], Apple Inc.</ref>

Swift also has limited support for ''attributes'', metadata that is read by the development environment, and is not necessarily part of the compiled code. Like Objective-C, attributes use the <code>@</code> syntax, but the currently available set is small. One example is the <code>@IBOutlet</code> attribute, which marks a given value in the code as an ''outlet'', available for use within [[Software:Interface Builder|Interface Builder]] (IB). An ''outlet'' is a device that binds the value of the on-screen display to an object in code.

On non-Apple systems, Swift does not depend on an Objective-C runtime or other Apple system libraries; a set of Swift "Corelib" implementations replace them. These include a "swift-corelibs-foundation" to stand in for the [[Organization:Foundation Kit|Foundation Kit]], a "swift-corelibs-libdispatch" to stand in for the Grand Central Dispatch, and an "swift-corelibs-xctest" to stand in for the XCTest APIs from [[Software:Xcode|Xcode]].<ref>{{cite web |title=Apple: search "corelib" |url=https://github.com/apple?utf8=%E2%9C%93&q=corelibs&type=&language= |website=GitHub |language=en}}</ref>

As of 2019, with Xcode 11, Apple has also added a major new UI paradigm called SwiftUI.  SwiftUI replaces the older [[Software:Interface Builder|Interface Builder]] paradigm with a new declarative development paradigm.<ref>{{Cite web|title=Xcode - SwiftUI- Apple Developer|url=https://developer.apple.com/xcode/swiftui/|access-date=2021-02-01|website=developer.apple.com|language=en}}</ref>

=== Memory management ===
Swift uses [[Automatic Reference Counting]] (ARC) to [[Memory management|manage memory]]. Every instance of a class or closure maintains a reference count which keeps a running tally of the number of references the program is holding for on to. When this count reaches 0 the instance is deallocated. This automatic deallocation removes the need for a garbage collector as instances are deallocated as soon as they are no longer needed.

A ''[[Reference counting#reference cycle|strong reference cycle]]'' can occur if two instances each strongly reference each other (e.g. A references B, B references A). Since neither instances reference count can ever reach zero neither is ever deallocated, resulting in a [[Memory leak|memory leak]]. Swift provides the keywords <code>weak</code> and <code>unowned</code> to prevent strong reference cycles. These keywords allow an instance to be referenced without incrementing its reference count. <code>weak</code> references must be optional variables, since they can change and become <code>nil</code>.<ref name="Intermediate Swift2">{{cite web |last1=Lanier |first1=Brian |last2=Groff |first2=Joe |title=Intermediate Swift |url=https://developer.apple.com/videos/wwdc/2014/?include=403#403 |access-date=July 3, 2014 |publisher=Apple}}</ref> Attempting to access an <code>unowned</code> value that has already been deallocated results in a runtime error.

A closure within a class can also create a strong reference cycle by capturing self references. Self references to be treated as weak or unowned can be indicated using a ''capture list.''<source lang="swift" line="1">
class Person {
    let name: String
    weak var home: Home? // Defined as a weak reference in order to break the reference cycle. weak references do not increment the reference count of the instance that they refer to.
    
    init(name: String) {
        self.name = name
    }
    
    deinit { print("De-initialized \(name)") }
}

class Home {
    let address: String
    var owner: Person?
    
    init(address: String, owner: Person?) {
        self.address = address
        self.owner = owner
    }
    
    deinit { print("De-initialized \(address)") }
}

var stacy: Person? = Person(name: "Stacy")
var house21b: Home? = Home(address: "21b Baker Street", owner: stacy)

stacy?.home = house21b // stacy and house42b now refer to each other.

stacy = nil // The reference count for stacy is now 1, because house21b is still holding a reference to it. 
house21b = nil // house21b's reference count drops to 0, which in turn drops stacy's count to 0 because house21b was the last instance holding a strong reference to stacy.

// Prints:
// De-initialized 21b Baker Street
// De-initialized Stacy
</source>

=== Debugging ===
A key element of the Swift system is its ability to be cleanly debugged and run within the development environment, using a [[Read–eval–print loop|read–eval–print loop]] (REPL), giving it interactive properties more in common with the scripting abilities of Python than traditional [[System programming|system programming]] languages. The REPL is further enhanced with [[Software:Swift Playgrounds|playgrounds]], interactive views running within the Xcode environment or [[Software:Playgrounds (Xcode feature)|Playgrounds]] app that respond to code or debugger changes on-the-fly.<ref>{{cite magazine|last1=Metz|first1=Cade|title=Why Coders Are Going Nuts Over Apple's New Programming Language|url=https://www.wired.com/2014/06/apple-swift-language/|magazine=Wired|access-date=July 16, 2014}}</ref> Playgrounds allow programmers to add in Swift code along with markdown documentation. Programmers can step through code and add breakpoints using [[Software:LLDB (debugger)|LLDB]] either in a console or an [[Integrated development environment|IDE]] like Xcode.

== Comparisons to other languages ==

Swift is considered a [[List of C-family programming languages|C family programming language]] and is similar to C in various ways:

* Most operators in C also appear in Swift, although some operators such as <code>+</code> have slightly different behavior. For example, <code>+</code> in Swift traps on overflow, whereas <code>&+</code> is used to denote the C-like behavior of wrapping on overflow.
* Curly braces are used to group statements.
* Variables are assigned using an [[Equals sign|equals sign]], but compared using [[==|two consecutive equals signs]]. A new identity operator, ===, is provided to check if two data elements refer to the same object.
* Control statements <code>while</code>, <code>if</code>, and <code>switch</code> are similar, but have extended functions, e.g., a <code>switch</code> that takes non-integer cases, <code>while</code> and <code>if</code> supporting [[Pattern matching|pattern matching]] and conditionally unwrapping optionals, <code>for</code> uses the {{code|1=for i in 1...10|2=swift}} syntax.
* Square brackets are used with [[Array data structure|arrays]], both to declare them and to get a value at a given index in one of them.

It also has similarities to Objective-C:

* Basic numeric types (<code>Int, UInt, Float, Double</code>)
* Class methods are inherited, like instance methods; <code>self</code> in class methods is the class the method was called on.
* Similar <code>for</code>...<code>in</code> enumeration syntax.

Differences from Objective-C include:

* Statements do not need to end with semicolons (<code>;</code>), though these must be used to allow more than one statement on a line.
* No header files.
* Uses [[Type inference|type inference]].
* [[Generic programming]].
* Functions are first-class objects.
* Enumeration cases can have associated data ([[Algebraic data type|algebraic data type]]s).
* Operators can be redefined for classes ([[Operator overloading|operator overloading]]), and new operators can be defined.
* Strings fully support [[Unicode]]. Most Unicode characters can be used in either identifiers or operators.
* No [[Exception handling|exception handling]]. Swift 2 introduces a different and incompatible error-handling model.<ref>{{cite web|url=https://stackoverflow.com/a/26749528|title=Error-Handling in Swift-Language|work=stackoverflow.com}}</ref>
* Several features of earlier [[List of C-family programming languages|C-family languages]] that are easy to misuse have been removed:
** [[Pointer (computer programming)|Pointers]] are not exposed by default. There is no need for the programmer to keep track of and mark names for referencing or dereferencing.
** Assignments return no value. This prevents the common error of writing <code>i = 0</code> instead of <code>i == 0</code> by throwing a compile-time error.
** No need to use <code>break</code> statements in <code>[[Switch statement|switch]]</code> blocks. Individual cases do not fall through to the next case unless the <code>fallthrough</code> statement is used.
** Variables and constants are always initialized and array bounds are always checked.
** [[Integer overflow]]s, which result in [[Undefined behavior|undefined behavior]] for signed integers in C, are trapped as a run-time error in Swift. Programmers can choose to allow overflows by using the special arithmetical operators <code>&+</code>, <code>&-</code>, <code>&*</code>, <code>&/</code> and <code>&%</code>. The properties <code>min</code> and <code>max</code> are defined in Swift for all integer types and can be used to safely check for potential overflows, versus relying on constants defined for each type in external libraries.
** The one-statement form of <code>if</code> and <code>while</code>, which allows for the omission of braces around the statement, is unsupported.
** C-style enumeration <code>for (int i = 0; i < c; i++)</code>, which is prone to [[Off-by-one error|off-by-one error]]s, is unsupported (from Swift 3 onward).<ref>{{Cite web|url=https://github.com/apple/swift-evolution/blob/master/proposals/0007-remove-c-style-for-loops.md|title=apple/swift-evolution|website=GitHub|access-date=April 4, 2016}}</ref>
** The pre- and post- [[Increment and decrement operators|increment and decrement operators]] (<code>i++</code>, <code>--i</code> ...) are unsupported (from Swift 3 onward), more so since C-style <code>for</code> statements are also unsupported from Swift 3 onward.<ref>{{Cite web|url=https://github.com/apple/swift-evolution/blob/master/proposals/0004-remove-pre-post-inc-decrement.md|title=apple/swift-evolution|website=GitHub|access-date=April 4, 2016}}</ref>

== Development and other implementations ==

Because Swift can run on Linux, it is sometimes also used as a server-side language.<ref>{{Cite web|url=https://9to5mac.com/2016/02/22/ibm-swift-cloud-kitura/|title=IBM brings Swift to the cloud, releases web framework Kitura written in Apple's programming language|last=Barbosa|first=Greg|date=February 22, 2016|website=9to5Mac|access-date=May 16, 2016}}</ref> Some web frameworks have already been developed, such as [[Company:IBM|IBM]]'s [[Software:Kitura|Kitura]] (now discontinued), [[Software:Perfect (server framework)|Perfect]] and Vapor.

An official "Server APIs" work group has also been started by Apple,<ref>{{Cite news|url=https://swift.org/blog/server-api-workgroup/|title=Server APIs Work Group|date=October 25, 2016|newspaper=Swift.org|access-date=October 28, 2016}}</ref> with members of the Swift developer community playing a central role.<ref>{{Cite web|url=https://swift.org/server-apis/|title=Swift.org|website=Swift.org|access-date=October 28, 2016|archive-date=May 10, 2021|archive-url=https://web.archive.org/web/20210510193318/https://swift.org/server-apis/|url-status=dead}}</ref>

A second free implementation of Swift that targets Cocoa, [[Company:Microsoft|Microsoft]]'s [[Common Language Infrastructure]] (.NET), and the [[Software:Java (software platform)|Java]] and [[Software:Android (operating system)|Android]] platform exists as part of the ''Elements Compiler'' from RemObjects Software.<ref>{{Cite web|title = RemObjects Elements Compiler|url = https://www.elementscompiler.com/silver|access-date = January 17, 2016}}</ref>

By combining toolchains from LLVM and [[Software:Macintosh Programmer's Workshop|Macintosh Programmer's Workshop]], it is possible to run a very small subset of the language on [[Software:Mac OS 9|Mac OS 9]].<ref>{{cite web |last1=Rose |first1=Jordan |title=Swift on Mac OS 9 |url=https://belkadan.com/blog/2020/04/Swift-on-Mac-OS-9/ |website=-dealloc |date=1 April 2020}}</ref>

== See also ==
* [[Comparison of programming languages]]
* [[Objective-C]]
* [[D (programming language)]]
* [[Kotlin (programming language)]]
* [[Python (programming language)]]
* [[Nim (programming language)]]

== References ==
{{Reflist|30em}}

== External links ==
* [https://developer.apple.com/swift/ Swift] at [[Software:Apple Developer|Apple Developer]]
* {{GitHub|apple/swift|Swift's source code}}
* [https://iosexamples.com/ Swift Example]
* [https://vapor.codes/ Server-side Swift - The Vapor Framework]

{{Programming languages}}
{{Apple Software}}


[[Category:Declarative programming languages]]
[[Category:Object-oriented programming languages]]
[[Category:Pattern matching programming languages]]
[[Category:Programming languages]]
[[Category:Software using the Apache license]]
[[Category:Statically typed programming languages]]
[[Category:Systems programming languages]]

{{Sourceattribution|Swift (programming language)}}