hwnn_1_5.swift

struct AnimalReport {
    let animal: Animal
    func describe() {...}
}
struct AnimalSelection {
    let animals: [Animal]
    let animalReport: AnimalReport
    func selectAnimal(_ animal: Animal) {...}
}
let animals: [Animal] = [
    Dog(name: "Doggy", age: 5),
    Horse(name: "Horsy", age: 7)
]

let b = AnimalReport(animal: #Animal#) // Which animal??
let a = AnimalSelection(animals: animals, animalReport: b)

// Runtime
a.selectAnimal(animals[0])