Swift 4 builds on the strengths of Swift 3, delivering greater robustness and stability, providing source code compatibility with Swift 3, making improvements to the standard library, and adding features like smart key paths and serialization, all while shortening build times and reducing the size of app binaries.
Swift 4 was developed in the open at Swift.org, with source code, a bug tracker, mailing lists, and regular development builds available for everyone. This broad community of developers, both inside Apple as well as hundreds of outside contributors, work together to make Swift even more amazing. Swift already supports all Apple platforms as well as Linux, with community members actively working to port to even more platforms. We’re excited to see more ways in which Swift makes software safer and faster, while also making programming more fun.
To learn more about the open source Swift community, visit Swift.org