Real-world iOS engineering, explained clearly.
The third door out of 'I don't want to name the concrete type'. some hides one concrete type while keeping its identity — no box, compile-time. any erases the type into a runtime box. This is how you finally return a protocol that has an associatedtype.
One swapTwoValues, one Stack<Element>, one findIndex — written once, working for every type. Generics let the caller pick the concrete type, the compiler specialize the code, and the box from #13 disappear. Array, Dictionary, Optional, and Result were generic all along.
A protocol is a contract, not a class. It says what a type must do without saying what it is — and that single idea powers delegation, synthesized Equatable, existentials, and the protocol extensions that make Swift idiomatic.
throw, try, do/catch, defer, rethrows, Result, and Swift 6 typed throws. An error isn't a magic exception — it's just a value of a type that conforms to Error, routed through your call stack as cheaply as a return.
Swift's antidote to the billion-dollar mistake. Optional is just an enum — and nil, if let, guard let, ??, !, and optional chaining all compile down to checking which case you're in.
Subclassing, overriding, and super. Designated vs convenience initializers, two-phase initialization, failable and required init, and deinit — the full lifecycle of a class, explained in memory.
Stored vs computed properties, observers, lazy, static. How properties define the memory layout and why computed = zero storage.
Value semantics vs reference semantics, static vs dynamic dispatch, and why Apple recommends structs by default. The article that changes how you think about Swift.
Raw values, associated values, recursive enums with indirect, and how the compiler picks the minimal memory representation.
Closure expressions, value capturing, capture lists, @escaping vs non-escaping, and why closures are reference types that live on the heap.
