Swift - Wyatt's Notes

sources:

• text: Standard textbook reference

Swift is a programming language with a rich type system and ecosystem. These notes cover the language from fundamentals to advanced topics, with worked examples, practice problems, and flashcards.

Intuition

Swift is like a modern sports car: fast, safe, and comfortable. The type system protects you from crashes (both memory and logical), the syntax is clean and expressive, and the performance rivals lower-level languages. The optional system is like the car’s safety features: it forces you to check for dangers before they cause accidents.

These notes guide you from the driver’s seat (basic types and functions) to the engine room (concurrency and advanced patterns). Each chapter adds a new capability, like learning to use cruise control before tackling the racetrack. The goal is not just to drive, but to drive well.

Common Mistakes

Mistake 1: Force unwrapping optionals with !

Force unwrapping (value!) crashes the program if the optional is nil. Students often use ! to quickly unwrap optionals without checking for nil, leading to runtime crashes. Instead, use optional binding (if let value = optional), nil coalescing (value ?? defaultValue), or guard statements (guard let value = optional else { return }). Only force unwrap when you are absolutely certain the value is non-nil.

Mistake 2: Not handling errors with do-try-catch

Swift’s error handling uses the do-try-catch pattern. Students sometimes call throwing functions without try or without wrapping them in a do block, leading to compile errors. The correct pattern is do { try someThrowingFunction() } catch { handleError(error) }. Alternatively, use try? to silently convert errors to nil, or try! to assert the function will not throw (crashes if it does).

Mistake 3: Creating retain cycles with strong reference captures in closures

When a closure captures self strongly, it creates a retain cycle: the object holds the closure, and the closure holds the object, preventing deallocation. Students often write closure = { self.doSomething() } without thinking about memory. Use capture lists to break the cycle: closure = { [weak self] in self?.doSomething() } or [unowned self] when you know self will not be nil during the closure’s lifetime.

Topics

Cross-References

• Swift Introduction - Language overview and modern Swift features
• Variables and Types - Type system including optionals and type inference
• Error Handling - do-try-catch patterns and optional-based error propagation