Application development in today's world is not just about building for one platform. Modern applications have an ecosystem of apps that run on multiple devices and platforms. In order for these apps to run on the multiple platforms they also need a server-side component to be able to seamlessly save and retrieve data so that a user can switch between them and start using the app from where they left off on another platform. To make these modern applications possible, developers write code on the different technology stacks that have different programming languages and frameworks/libraries. This makes the job of the developer especially difficult due to the context switching between programming languages when building the application.

In the world of the web, developers have enjoyed working on the frontend web applications using JavaScript but after the introduction of Node.js, web developers who were mainly focused on the frontend could finally work on the backend in a language that feels familiar. Web developers have embraced the idea of working across different technology stacks as part of their app development because they can now write the frontend in JavaScript and use the same language to build server-side components.

Similarly, Swift, which is popular in the world of iOS, tvOS, and macOS for building rich client-facing applications, is now available on server-side thanks to Apple. Like JavaScript developers, Swift developers can now finally build server-side components in a language that is familiar to them while they continue to build frontend applications for different platforms, such as mobile, watch, TV, or desktop. Currently Swift is gaining popularity on the server-side, and it has never been a good time to be Swift developers. We can now engage ourselves in true full stack app development by working on different platforms using the same language and standard libraries that we are familiar with when building iOS, tvOS, watchOS, and macOS applications.

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.

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.

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.

There are several benefits of using Swift on the server side. Some of them include:

• Being able to work on a feature as a whole: Being able to work on an entire feature helps deliver the feature on time and as expected. Traditionally, teams are divided into frontend and backend teams but if you have the same language used for both front and backend then it will help developers contribute to the entire stack. Developers working on building the app can create the API endpoints needed to avoid the unnecessary back and forth between developers and prevent an app developer from being blocked by the backend engineer and move the feature development forward.
• Working with familiar language and tools: Working with a familiar language reduces the biggest hurdle to working across different stacks. You can build both mobile and server-side components using the same language and tools. Swift developers can use their favorite IDE, Xcode, to build their backend server and do not have to learn new tools or install different IDEs.
• Sharing code base: Code shareability is another big win for using Swift as you can share models, validations, and business logic easily across platforms. Not having to rewrite the same logic in different languages saves times and helps avoid expensive bugs caused by inconsistencies introduced by different developers who might have worked on rewriting the business logic on a different stack.
• Leveraging great APIs: Apple did a great job building easy-to-use APIs on their platform and now being able to use those APIs server-side is a big benefit for developers as they do not have to learn new standard libraries or reinvent them on the Linux platform.