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The Swift Programming Language

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# Swift Programming Language

Welcome to Swift!

Swift is a high-performance system programming language. It has a clean and modern syntax, offers seamless access to existing C and Objective-C code and frameworks, and is memory safe (by default).

Although inspired by Objective-C and many other languages, Swift is not itself a C-derived language. As a complete and independent language, Swift packages core features like flow control, data structures, and functions, with high-level constructs like objects, protocols, closures, and generics. Swift embraces modules, eliminating the need for headers and the code duplication they entail.


To read the documentation, start by installing the Sphinx documentation generator tool (just run easy_install -U Sphinx from the command line and you're good to go). Once you have that, you can build the Swift documentation by going into docs and typing make. This compiles the .rst files in the docs directory into HTML in the docs/_build/html directory.

Once built, the best place to start is with the Swift white paper, which gives a tour of the language (in docs/_build/html/whitepaper/index.html). Another potentially useful document is docs/LangRef, which gives a low level tour of how the language works from the implementation perspective.

Many of the docs are out of date, but you can see some historical design documents in the docs directory.

Another source of documentation is the standard library itself, located in stdlib. Much of the language is actually implemented in the library (including Int), and the standard library gives some examples of what can be expressed today.

Getting Started

These instructions give the most direct path to a working Swift development environment. Options for doing things differently are discussed below.

System Requirements

OS X, Ubuntu Linux LTS, and the latest Ubuntu Linux release are the current supported host development operating systems.

For OS X, you need the latest Xcode.

For Ubuntu, you'll need the following development dependencies:

sudo apt-get install git cmake ninja-build clang uuid-dev libicu-dev icu-devtools libbsd-dev libedit-dev libxml2-dev libsqlite3-dev swig libpython-dev libncurses5-dev pkg-config

Note: LLDB currently requires at least swig-1.3.40 but will successfully build with version 2 shipped with Ubuntu.

If you are building on Ubuntu 14.04 LTS, you'll need to upgrade your clang compiler for C++14 support and create a symlink:

 sudo apt-get install clang-3.6
 sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-3.6 100
 sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-3.6 100

Getting Sources for Swift and Related Projects

For those checking out sources as read-only:

 git clone swift
 git clone llvm
 git clone clang
 git clone lldb
 git clone cmark
 git clone llbuild
 git clone swiftpm
 git clone
 git clone

For those who plan on regularly making direct commits, cloning over SSH may provide a better experience (which requires uploading SSH keys to GitHub):

 git clone swift
 git clone llvm
 git clone clang
 git clone lldb
 git clone cmark
 git clone llbuild
 git clone swiftpm
 git clone
 git clone

CMake is the core infrastructure used to configure builds of Swift and its companion projects; at least version is required. Your favorite Linux distribution likely already has a CMake package you can install. On OS X, you can download the CMake Binary Distribution, bundled as an application, copy it to /Applications, and add the embedded command line tools to your PATH:

export PATH=/Applications/$PATH

Ninja is the current recommended build system for building Swift and is the default configuration generated by CMake. If you're on OS X or don't install it as part of your Linux distribution, clone it next to the other projects and it will be bootstrapped automatically:

git clone


git clone

You can also install CMake and Ninja on OS X using a third-party packaging tool like Homebrew

brew install cmake ninja

…or MacPorts.

sudo port install cmake ninja

Building Swift

The build-script is a high-level build automation script that supports basic options such as building a Swift-compatible LLDB, building the Swift Package Manager, building for iOS, running tests after builds, and more. It also supports presets which you can define for common combinations of build options.

To find out more:

utils/build-script -h

Note: Arguments after "--" above are forwarded to build-script-impl, which is the ultimate shell script that invokes the actual build and test commands.

A basic command to build Swift and run basic tests with Ninja:

utils/build-script -t

Developing Swift in Xcode

The Xcode IDE can be used to edit the Swift source code, but it is not currently fully supported as a build environment for SDKs other than OS X. If you'd like to build for other SDKs but still use Xcode, once you've built Swift using Ninja or one of the other supported CMake generators, you can set up an IDE-only Xcode environment using the build-script's -X flag:

utils/build-script -X --skip-build -- --reconfigure

The --skip-build flag tells build-script to only generate the project, not build it in its entirety. A bare minimum of LLVM tools will build in order to configure the Xcode projects.

The --reconfigure flag tells build-script-impl to run the CMake configuration step even if there is a cached configuration. As you develop in Xcode, you may need to rerun this from time to time to refresh your generated Xcode project, picking up new targets, file removals, or file additions.

Testing Swift

See docs/Testing.rst.

Contributing to Swift

Contributions to Swift are welcomed and encouraged! Please see the Contributing to Swift guide.

To be a truly great community, needs to welcome developers from all walks of life, with different backgrounds, and with a wide range of experience. A diverse and friendly community will have more great ideas, more unique perspectives, and produce more great code. We will work diligently to make the Swift community welcoming to everyone.

To give clarity of what is expected of our members, Swift has adopted the code of conduct defined by the Contributor Covenant. This document is used across many open source communities, and we think it articulates our values well. For more, see the website.


The Swift Programming Language

License:Apache License 2.0


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