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Foundation

The Foundation framework defines a base layer of functionality that is required for almost all applications. It provides primitive classes and introduces several paradigms that define functionality not provided by either the Objective-C runtime and language or Swift standard library and language.

It is designed with these goals in mind:

  • Provide a small set of basic utility classes and data structures.
  • Make software development easier by introducing consistent conventions.
  • Support internationalization and localization, to make software accessible to users around the world.
  • Provide a level of OS independence, to enhance portability.

There is more information on the Foundation framework here.

This project, swift-corelibs-foundation, provides a compatibility implementation of the Foundation API for platforms where there is no Objective-C runtime. On macOS, iOS, and other Apple platforms, apps should use the Foundation that comes with the operating system.

Project Navigator

Foundation builds in different configurations and is composed of several projects.

  graph TD;
      FF[Foundation.framework]-->SF
      subgraph GitHub
        SCLF[swift-corelibs-foundation]-->SF
        SF[swift-foundation]-->FICU[swift-foundation-icu]
        SF-->SC[swift-collections]
      end
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Swift Foundation

A shared library shipped in the Swift toolchain, written in Swift. It provides the core implementation of many key types, including URL, Data, JSONDecoder, Locale, Calendar, and more in the FoundationEssentials and FoundationInternationalization modules. Its source code is shared across all platforms.

swift-foundation depends on a limited set of packages, primarily swift-collections and swift-syntax.

Swift Corelibs Foundation

A shared library shipped in the Swift toolchain. It provides compatibility API for clients that need pre-Swift API from Foundation. It is written in Swift and C. It provides, among other types, NSObject, class-based data structures, NSFormatter, and NSKeyedArchiver. It re-exports the FoundationEssentials and FoundationInternationalization modules, allowing compatibility for source written before the introduction of the swift-foundation project. As these implementations are distinct from those written in Objective-C, the compatibility is best-effort only.

swift-corelibs-foundation builds for non-Darwin platforms only. It installs the Foundation umbrella module, FoundationXML, and FoundationNetworking.

Foundation ICU

A private library for Foundation, wrapping ICU. Using a standard version of ICU provides stability in the behavior of our internationalization API, and consistency with the latest releases on Darwin platforms. It is imported from the FoundationInternationalization module only. Clients that do not need API that relies upon the data provided by ICU can import FoundationEssentials instead.

Foundation Framework

A framework built into macOS, iOS, and all other Darwin platforms. It is written in a combination of C, Objective-C, and Swift. The Foundation framework compiles the sources from swift-foundation into its binary and provides one Foundation module that contains all features.

Using Foundation

Here is a simple main.swift file which uses Foundation. This guide assumes you have already installed a version of the latest Swift binary distribution.

import Foundation

// Make a URLComponents instance
let swifty = URLComponents(string: "https://swift.org")!

// Print something useful about the URL
print("\(swifty.host!)")

// Output: "swift.org"

You will want to use the Swift Package Manager to build your Swift apps.

Working on Foundation

swift-corelibs-foundation builds as a standalone project using Swift Package Manager. Simply use swift build in the root of the checkout to build the project.

swift-corelibs-foundation also builds as part of the toolchain for non-Darwin platforms. Instructions on building the toolchain are available in the Swift project.

Contributions

We welcome contributions to Foundation! Please see the known issues page if you are looking for an area where we need help. We are also standing by on the mailing lists to answer questions about what is most important to do and what we will accept into the project.