What are Swift generics?
Why Interviewers Ask This
This is a classic screening question for Swift & iOS roles. Hiring managers ask it early in interviews to gauge your baseline understanding and determine if you can communicate technical concepts clearly.
Answer
Generics allow writing flexible, reusable functions and types that work with any type, subject to defined constraints. They enable type-safe code without code duplication. Generic function: func swap<T>(_ a: inout T, _ b: inout T) { let temp = a; a = b; b = temp } var x = 5, y = 10 swap(&x, &y) // x=10, y=5 var s1 = "hello", s2 = "world" swap(&s1, &s2) // Works with any type!. Generic type: struct Stack<Element> { private var items: [Element] = [] mutating func push(_ item: Element) { items.append(item) } mutating func pop() -> Element? { return items.popLast() } var top: Element? { items.last } } var intStack = Stack<Int>() intStack.push(1); intStack.push(2) var stringStack = Stack<String>(). Type constraints: func findMax<T: Comparable>(_ array: [T]) -> T? { array.max() } // Multiple constraints: func process<T: Hashable & Equatable>(_ items: [T]) { }. Associated types in protocols: protocol Queue { associatedtype Element mutating func enqueue(_ item: Element) mutating func dequeue() -> Element? }. Where clauses: func merge<T: Sequence, U: Sequence>(_ a: T, _ b: U) -> [T.Element] where T.Element == U.Element { }. Opaque types (some): func makeContainer() -> some Container { // Return type is hidden }. Generics + protocols = Swift's powerful type system for expressing abstractions.
Common Mistake
A common mistake is memorizing definitions without understanding implications. When asked this question, go one level deeper — explain what happens when this concept is misused or ignored.