Design protocol interfaces in Swift

Swift_5.7_Generics

//
//  File.swift
//  SP
//
//  Created by Yevgen Sagidulin on 12.06.2022.
//

import Foundation

protocol AnimalFeed {
    associatedtype CropType: Crop where CropType.FeedType == Self
    static func grow() -> CropType
}

protocol Crop {
    associatedtype FeedType: AnimalFeed where FeedType.CropType == Self
    func harvest() -> FeedType
}


struct Alfalfa: Crop {
    func harvest() -> Hay {
        print("Alfalfa harverst -> Hay 🧻")
        return Hay()
    }
}

struct Hay: AnimalFeed {
    static func grow() -> Alfalfa {
        print("Alfalfa grow 🌿")
        return Alfalfa()
    }
}

struct GrassBucket: AnimalFeed {
    static func grow() -> Grass {
        print("Gtass grow 🌱")
        return Grass()
    }
}

struct Grass: Crop {
    func harvest() -> GrassBucket {
        print("Just making grass bucket out of grass 💐")
        return GrassBucket()
    }
}

protocol Animal {
    associatedtype Feed: AnimalFeed
    
    func eat(_ food: Feed)
}

struct Horse: Animal {
    func eat(_ food: Hay) {
        print("horse eating \(food)")
    }
}

struct Rebbit: Animal {
    func eat(_ food: GrassBucket) {
        print("rebbit eating \(food)")
    }
}


struct Farm {
    func feed(_ animal: some Animal) {
        let crop = type(of: animal).Feed.grow()
        let food = crop.harvest()
        animal.eat(food)
    }
    
    // This works only in app (bug in Playground)
//    func feedAll_swift60(_ animals: [any Animal]) {
//        animals.forEach { feed($0) }
//    }
    
    func feedAll_swift57(_ animals: [any Animal]) {
        animals.forEach { animal in
            if animal is Horse {
                feed(Horse())
            } else if animal is Rebbit {
                feed(Rebbit())
            }
        }
    }
}


let animals: [any Animal] = [
    Horse(),
    Horse(),
    Rebbit(),
]

let farm = Farm()
farm.feedAll_swift57(animals)