Code sample #3 from https://medium.com/@johnsundell/simple-swift-dependency-injection-with-functions-7b0ec5b49e60

Simple-Swift-dependency-injection-with-functions-2.swift

class CardGame {
    typealias Randomizer = (UInt32) -> UInt32
    
    private let deck: Deck
    private let randomizer: Randomizer
    
    init(deck: Deck, randomizer: @escaping Randomizer = arc4random_uniform) {
        self.deck = deck
        self.randomizer = randomizer
    }
    
    func drawRandomCard() -> Card {
        let index = randomizer(deck.count)
        let card = deck[index]
        return card
    }
}