Open source

In December 2015, Apple announced that it would open source Swift; this opened up the possibility of writing applications in Swift on other platforms, especially Linux. Open sourcing Swift meant that anyone could take the Swift code base and build a Swift compiler and toolset on their host operating system (OS) where LLVM is supported. This is exactly what Apple did soon after Swift was open sourced by creating Swift toolset that worked on Ubuntu, a popular distribution of Linux. Apple kept its promise of truly open sourcing Swift by also porting its libraries and frameworks, including Foundation, which is used extensively in iOS and macOS platforms, and made them work on Ubuntu. Without these frameworks, it would be hard to build cross-platform applications in Swift that work on both Apple's OS and Linux with same feature parity since Foundation is the standard library that contains access to essential data types, collections, and operating system services to define the base layer of functionality for any application.