A Swift Tour: Explore Swift’s features and design

Key Takeaways

• Swift is modern, expressive, and safe

• Prefer value types & immutability

• Errors & optionals handle every case

• Protocols & generics for abstractions

• Data-race safe concurrency

Core features of Swift

Value types

• Don’t share state → changing one value can’t affect other values

• Equal values are interchangeable (no identity)

• Used for the basic types in Swift

Errors and Optionals

• Errors should be clearly marked and carry actionable context

• Swift differentiates recoverable errors from programmer mistakes

• throws / try make error handling explicit

• Optionals represent a value that may be nil → must be unwrapped before use

• Both force code to handle all the possibilities

Code organization (modules and packages)

• Module: a collection of source files always built together

• Package: a distributable collection of modules

• Swift Package Manager (SwiftPM): the tool for managing packages & dependencies

• Access control levels: private, internal, package, public

Classes

• Represent shared mutable state (reference type, has identity)

• Support single inheritance; subclasses can override superclass methods

• Use for shared mutable state, identity, or inheritance

• Memory managed automatically (ARC) → watch for reference cycles, break them with weak

Protocols and generics

• General way to build abstractions - work with both value and reference types

• Protocol: an abstract set of requirements for a type

• Generics: write reusable, type-safe code across families of types (with constraints, e.g. where Element: Hashable)

• See more Embrace Swift generics, Design protocol interfaces in Swift

Concurrency

• Task: the fundamental unit of concurrency (a concurrent execution context)

• Model suspension in code:

  • async: a function that may suspend

  • await: marks where suspension can occur

• Sendable: types safe to share across concurrency domains

• actor: a reference type that automatically protects its shared mutable state by serializing access

• Swift 6 verifies data-race safety at compile time

• Learning starting point: Explore structured concurrency in Swift

Extensibility

• Property wrapper: encapsulate logic for managing a stored value

• Result builder: express complex values declaratively

  • See more Write a DSL in Swift using result builders

• Macro: a compiler plugin that takes a syntax tree as input and returns transformed code as output

  • See more Expand on Swift macros