Swift

Modern

Swift is the result of the latest research on programming languages, combined with decades of experience building software that runs on billions of devices. Named parameters are expressed in a clean syntax that makes APIs in Swift easy to read and maintain. Even better, you don’t even need to type semi-colons. Inferred types make code cleaner and less prone to mistakes, while modules eliminate headers and provide namespaces. To best support international languages and emoji, strings are Unicode-correct and use a UTF-8-based encoding to optimize performance for a wide variety of use cases. Memory is managed automatically using tight, deterministic reference counting, keeping memory usage to a minimum without the overhead of garbage collection. You can even write concurrent code with simple, built-in keywords that define asynchronous behavior, making your code more readable and less error prone.

struct Player {
    var name: String
    var highScore: Int = 0
    var history: [Int] = []

    init(_ name: String) {
        self.name = name
    }
}

var player = Player("Tomas")

Declare new types with modern, straightforward syntax. Provide default values for instance properties and define custom initializers.

extension Player {
    mutating func updateScore(_ newScore: Int) {
        history.append(newScore)
        if highScore < newScore {
            print("\(newScore)! A new high score for \(name)! 🎉")
            highScore = newScore
        }
    }
}

player.updateScore(50)
// Prints "50! A new high score for Tomas! 🎉"
// player.highScore == 50

Add functionality to existing types using extensions, and cut down on boilerplate code with custom string interpolations.

extension Player: Codable, Equatable {}

import Foundation
let encoder = JSONEncoder()
try encoder.encode(player)

print(player)
// Prints "Player(name: "Tomas", highScore: 50, history: [50])”

Quickly extend your custom types to take advantage of powerful language features, such as automatic JSON encoding and decoding.

let players = getPlayers()

// Sort players, with best high scores first
let ranked = players.sorted(by: { player1, player2 in
    player1.highScore > player2.highScore
})

// Create an array with only the players’ names
let rankedNames = ranked.map { $0.name }
// ["Erin", "Rosana", "Tomas"]

Perform powerful custom transformations using streamlined closures.

These forward-thinking concepts result in a language that’s fun and easy to use.

Swift has many other features to make your code more expressive:

• Generics that are powerful and simple to use
• Protocol extensions that make writing generic code even easier
• First-class functions and a lightweight closure syntax
• Fast and concise iteration over a range or collection
• Tuples and multiple return values
• Structs that support methods, extensions, and protocols
• Enums can have payloads and support pattern matching
• Functional programming patterns, e.g., map and filter
• Macros that help reduce boilerplate code
• Built-in error handling using try / catch / throw

Designed for safety

Swift eliminates entire classes of unsafe code. Variables are always initialized before use, arrays and integers are checked for overflow, memory is automatically managed, and potential data races can be spotted at compile-time. Syntax is tuned to make it easy to define your intent — for example, simple three-character keywords define a variable ( var ) or constant ( let ). And Swift heavily leverages value types, especially for commonly used types like Arrays and Dictionaries. This means that when you make a copy of something with that type, you know it won’t be modified elsewhere.

Another safety feature is that by default Swift objects can never be nil. In fact, the Swift compiler will stop you from trying to make or use a nil object with a compile-time error. This makes writing code much cleaner and safer, and prevents a huge category of runtime crashes in your apps. However, there are cases where nil is valid and appropriate. For these situations Swift has an innovative feature known as optionals. An optional may contain nil, but Swift syntax ensures you to safely deal with it using the ? syntax to indicate to the compiler you understand the behavior and will handle it safely.

extension Collection where Element == Player {
    // Returns the highest score of all the players,
    // or `nil` if the collection is empty.
    func highestScoringPlayer() -> Player? {
        return self.max(by: { $0.highScore < $1.highScore })
    }
}

Use optionals when you might have an instance to return from a function, or you might not.

if let bestPlayer = players.highestScoringPlayer() {
    recordHolder = """
        The record holder is \(bestPlayer.name),\
        with a high score of \(bestPlayer.highScore)!
        """
} else {
    recordHolder = "No games have been played yet."
}
print(recordHolder)
// The record holder is Erin, with a high score of 271!

let highestScore = players.highestScoringPlayer()?.highScore ?? 0
// highestScore == 271

Features such as optional binding, optional chaining, and nil coalescing let you work safely and efficiently with optional values.

Fast and powerful

From its earliest conception, Swift was built to be fast. Using the incredibly high-performance LLVM compiler technology, Swift code is transformed into optimized machine code that gets the most out of modern hardware. The syntax and standard library have also been tuned to make the most obvious way to write your code also perform the best whether it runs in the watch on your wrist or across a cluster of servers.

Swift is a successor to the C, C++, and Objective-C languages. It includes low-level primitives such as types, flow control, and operators. It also provides object-oriented features such as classes, protocols, and generics.

Great first language

Swift can open doors to the world of coding. In fact, it was designed to be anyone’s first programming language, whether you’re still in school or exploring new career paths. For educators, Apple created free curriculum to teach Swift both in and out of the classroom. First-time coders can download Swift Playgrounds — an app for iPad and Mac that makes getting started with Swift code interactive and fun.

Aspiring app developers can access free courses to learn to build their first apps in Xcode. And Apple Stores around the world host Today at Apple Coding & Apps sessions where you can get practical experience with Swift code.

Learn more about Swift education resources from Apple

Playgrounds and Read-Eval-Print-Loop (REPL)

Much like Swift Playgrounds for iPad and Mac, playgrounds in Xcode make writing Swift code incredibly simple and fun. Type a line of code and the result appears immediately. You can then Quick Look the result from the side of your code, or pin that result directly below. The result view can display graphics, lists of results, or graphs of a value over time. You can open the Timeline Assistant to watch a complex view evolve and animate, great for experimenting with new UI code, or to play an animated SpriteKit scene as you code it. When you’ve perfected your code in the playground, simply move that code into your project. Swift is also interactive when you use it in Terminal or to the Xcode LLDB debugging console.

Package manager

Swift Package Manager is a cross-platform tool for building, running, testing, and packaging your Swift libraries and executables. Swift packages are the best way to distribute libraries and source code to the Swift community. Configuration of packages is written in Swift itself, making it easy to configure targets, declare products, and manage package dependencies. Swift packages can also include custom commands that help build your projects and provide additional tooling. Swift Package Manager itself is actually built with Swift and included in the Swift open source project as a package.

Objective-C and C++ interoperability

You can create an entirely new application with Swift today, or begin using Swift code to implement new features and functionality in your app. Swift code coexists along side your existing Objective-C and C++ files in the same project, with access to your Objective-C and C++ APIs, making it easy to adopt.