Associated types: Generic Protocol in Swift

In Swift, a protocol can be made generic by using associated types. Associated types give a placeholder name to a type that is used as part of the protocol. The actual type to use for that associated type isn’t specified until the protocol is adopted.

protocol Addition {
    associatedtype Item
    
    init(element1: Item, element2: Item)
    func add() -> Item
}

struct IntAddition: Addition {
    typealias Item = Int
    private let element1: Int
    private let element2: Int
    
    init(element1: Int, element2: Int) {
        self.element1 = element1
        self.element2 = element2
    }
    
    func add() -> Int {
        return element1 + element2
    }
}

protocol Numeric {
    static func +(lhs: Self, rhs: Self) -> Self
}

extension Int: Numeric {}
extension Double: Numeric {}

struct GenericAddition<T: Numeric>: Addition {
    private let element1: T
    private let element2: T
    
    init(element1: T, element2: T) {
        self.element1 = element1
        self.element2 = element2
    }
    
    func add() -> T {
        return element1 + element2
    }
}

let testDouble = GenericAddition(element1: 3.5, element2: 2.9)
testDouble.add() // 6.4

let testInt = GenericAddition(element1: 3, element2: 2)
testInt.add() // 5

Next Post — https://medium.com/@abhinay.mca09/create-a-generic-protocol-for-uitableview-data-source-9c7666565809

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