Swift — Generics

Generic functions

func swapTwo<T>(_ a: inout T, _ b: inout T) {
    let temp = a
    a = b
    b = temp
}

var x = 1, y = 2
swapTwo(&x, &y)
print(x, y) // 2 1

Generic types

struct Stack<Element> {
    private var items: [Element] = []

    mutating func push(_ item: Element) {
        items.append(item)
    }

    mutating func pop() -> Element? {
        items.popLast()
    }

    var count: Int { items.count }
}

var stack = Stack<Int>()
stack.push(1)
stack.push(2)
print(stack.pop() ?? 0) // 2

Type constraints

func findIndex<T: Equatable>(of value: T, in array: [T]) -> Int? {
    for (index, item) in array.enumerated() {
        if item == value {
            return index
        }
    }
    return nil
}

print(findIndex(of: 3, in: [1, 2, 3, 4])) // Optional(2)

Where clause

func process<T, U>(a: T, b: U) where T: Numeric, U: CustomStringConvertible {
    print("\(a) - \(b)")
}

process(a: 42, b: "hello")

Associated types

protocol Container {
    associatedtype Item
    mutating func push(_ item: Item)
    mutating func pop() -> Item?
}

Mini Practice

Write Swift code that:

1. Creates a generic Stack struct
2. Writes a generic function with type constraints
3. Uses a where clause
4. Defines a protocol with an associated type

Up Next

Congratulations! You've completed the Swift fundamentals. Continue exploring advanced topics like SwiftUI, Combine, and async/await.