What Swift Is and Where It Runs

Safe, fast and expressive

Swift is a compiled, statically typed language introduced by Apple in 2014 and open-sourced in 2015. It is the primary language for apps on iOS, iPadOS, macOS, watchOS, tvOS and visionOS, and it also runs on Linux and Windows, with growing use for server-side code and command-line tools. Swift's design goals are safety (no null pointer crashes thanks to optionals, bounds-checked arrays, definite initialisation, automatic memory management), speed (compiled to native code through LLVM) and expressiveness (type inference, closures, generics, protocol extensions, pattern matching). It interoperates with Objective-C and, increasingly, with C and C++. Swift 6 (2024) introduced a language mode with compile-time data-race safety, typed throws and more, and later releases continue to make concurrency more approachable. Swift evolves publicly through the Swift Evolution proposal process. For UI, Apple's modern framework is SwiftUI, while older apps use UIKit; this course focuses on the language itself, which every Apple-platform developer needs first.

One language, many platforms

Swift code compiles to native binaries for Apple platforms, Linux and Windows.

A first Swift program

Constants, inference, interpolation and a function call.

let name = "Asha"            // constant, type inferred as String
var visits = 0                // variable, inferred as Int
visits += 1

func greet(_ person: String, times: Int) -> String {
    "Hello, \(person)! You have visited \(times) time\(times == 1 ? "" : "s")."
}

print(greet(name, times: visits))

// command line:  swift run   (in a Swift package)  or  swift hello.swift

Learn the language before the UI framework

SwiftUI tutorials move fast and assume you understand optionals, structs, closures and protocols. A week on the language first makes SwiftUI far easier to follow.

Quick check: Which feature is central to Swift's safety against null-pointer crashes?

• Optionals that make the absence of a value explicit
• Garbage collection
• Manual memory management
• Dynamic typing