Swift's evolution

Swift started out as a general-purpose programming language, intended to replace Objective-C as the default language for building iOS, tvOS, watchOS, and macOS applications. Swift is a compiled language that compiles down to Low Level Virtual Machine (LLVM) bytecode and is Just-In-Time (JIT) compiled to native code of the architecture on its first run making Swift a very fast language. Swift also uses Automatic Reference Counting (ARC) to manage memory, making it simple to write applications especially for iOS where memory management is critical.

With all of these features, Swift definitely stands out from the rest of the languages popular during that time, which included Scala, Rust, Elixir, Kotlin, and C#. With growing popularity, all it needed was more platforms to run on and that is what Apple did when they open sourced it in late 2015.

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.

Server-side Swift

Since Swift is a language that is elegant and expressive while being performant, it was about time that it would be ported to run on a server-side platform. Building command-line tools with Swift become popular on the macOS platform soon after Apple made it easy to use Swift for general purpose programming outside of iOS app development with the use of the Hash Bang, #!, syntax specified on top of the Swift file just like in a scripting language such as Perl, Ruby, or Python. This made it very easy for anyone to write and run Swift code without having to compile it. The same technique works on Linux platform; so, let's see how it works:

1. Creating a Swift file called hello.swift
2. Adding the following code to the file:

#!/usr/bin/swift
print(“Hello World from Swift!”)

3. Making the file an executable by changing the permission on the file using chmod:

$ chmod +x hello.swift

4. Running the Swift code by typing the filename in the Terminal:

$ ./hello.swift

You should see Hello World from Swift! printed on the command line. This shows you how easy it is to create an executable in Swift without even having to compile it ahead of time; you can quickly test Swift code from the command line.