freeCodeCamp/guide/english/swift/generics/index.md

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Generics

Generics

Write a name inside angle brackets to make a generic function or type.

func makeArray<Item>(repeating item: Item, numberOfTimes: Int) -> [Item] {
	var result = [Item]()
	for _ in 0..<numberOfTimes {
		result.append(item)
	}
	return result
}
makeArray(repeating: "knock", numberOfTimes: 4)

You can make generic forms of functions and methods, as well as classes, enumerations, and structures.

// Reimplement the Swift standard library's optional type
	enum OptionalValue<Wrapped> {
		case none
		case some(Wrapped)
	}
	var possibleInteger: OptionalValue<Int> = .none
	possibleInteger = .some(100)

Use where right before the body to specify a list of requirements—for example, to require the type to implement a protocol, to require two types to be the same, or to require a class to have a particular superclass.

func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
where T.Element: Equatable, T.Element == U.Element
{
	for lhsItem in lhs {
		for rhsItem in rhs {
			if lhsItem == rhsItem {
			return true
			}
		}
	}
return false
}
anyCommonElements([1, 2, 3], [3])