Installing Swift from swift.org
If you are developing on and for the Apple platform, I strongly suggest that you stick with the version of Swift that comes with Xcode. Apple will not approve an app that was compiled using a version of Swift that is different than the one that came with the version of Xcode that you are using. This may seem a little extreme, but it ensures that the apps are compiled with a stable version of Swift and one that has been fully vetted to work with your version of Xcode.
If you are using one of the flavors of Linux that has pre-built binaries on the swift.org site, it is recommended that you use those. They are the easiest and quickest path to getting Swift up and running. You can also find complete installation instructions with a list of dependencies on the swift.org site under the Getting Started section.
If pre-built binaries are not provided for your flavor of Linux, if you want to try the latest version of Swift, or if you just want...