Language cheatsheet

Swift 6 Cheatsheet

Swift tooling and syntax: optionals, structs and enums, protocols, closures, error handling, async/await, actors and SwiftUI basics.

Tooling

Check the Swift version — Print the installed Swift toolchain version.
Create a package — Create a new command-line project with Swift Package Manager.
Build and run — Build the package, run it, and run its tests.
Run a script file — Run a Swift source file without building a project.
Add a dependency — Declare a package in Package.swift.

Constants and variables — let is constant and var can change. Types are inferred.
Handle optionals — Unwrap an optional safely with if let or guard let. ?? supplies a default.
Arrays and dictionaries — Collections are value types and use generic syntax.
Loops and switch — switch must be exhaustive and supports patterns and ranges.
Define functions — Argument labels make calls read like sentences. _ removes a label.
Closures — Pass behavior around. Trailing closure syntax reads cleanly.

Structs — Structs are value types with memberwise initializers. Mark mutating methods with mutating.
Classes — Classes are reference types and support inheritance.
Enums with associated values — Each case can carry its own data, and switch extracts it.
Protocols and extensions — A protocol describes requirements, and an extension adds default behavior.
Generics — Write a function once for any type that meets a constraint.
Encode and decode JSON — Conform to Codable and use JSONEncoder and JSONDecoder.

Throw and catch errors — Mark functions that can fail with throws, call them with try, and handle errors in do/catch.
Async functions — async functions can suspend. Call them with await.
Run work in parallel — async let starts child tasks that run concurrently.
Start a task — Task starts asynchronous work from synchronous code.
Protect shared state with an actor — An actor processes one call at a time, which prevents data races. Call its methods with await.
Update the UI on the main actor — Mark UI code @MainActor so it always runs on the main thread.

A simple view — A SwiftUI view returns its content from body. State changes re-render it.
Show a list — List and ForEach build rows from identifiable data.
Navigate between screens — NavigationStack with NavigationLink pushes detail screens.
Bind a control to state — A $ prefix passes a two-way binding to a control.
Load data when a view appears — The task modifier runs async work and cancels it when the view goes away.

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