All course materials are available at https://cs193p.stanford.edu.
The 3rd lecture of the 2025 version of Stanford's CS193p course (developing applications for iOS using SwiftUI). This lecture focuses on Swift's type system fundamentals and explains the Model-UI separation principle in SwiftUI, emphasizing that the Model contains the app's core logic and data (UI-independent) while the UI is a declarative, reactive visual manifestation of the Model. Covers the Swift type system, including: structs vs classes (value types vs reference types). Shows how enums can have associated data; generics for type-agnostic programming (like Array); how Optionals work; failable initializers that return Optionals; and extensions for adding functionality to existing types. Emphasizes Swift's strong typing, immutability by default, and the importance of clearly marking sources of truth with @State. All concepts are presented as building blocks for the CodeBreaker app development in the next lecture.
Paul Hegarty is a Lecturer who has been teaching CS193p at Stanford since 2010.