ServiceLocator.swift

//: Playground - noun: a place where people can play

protocol Cat {
    func meow() -> String
}

protocol Dog {
    func bark() -> String
}

class Smokey : Cat {
    func meow() -> String {
        return "Meeooow"
    }
}

class Buddy : Dog {
    func bark() -> String {
        return "Woof"
    }
}

protocol ServiceLocator {
    func getService<T>() -> T;
}

class Client {
    let cat : Cat
    let dog : Dog
    
    init(locator: ServiceLocator) {
        cat = locator.getService()
        dog = locator.getService()
    }
    
    func makeNoise() -> String {
        return "Cat goes \(cat.meow()), dog goes \(dog.bark())"
    }
}

protocol ServiceContainer {
    var locator: ServiceLocator {get}
    
    func registerService<T>(service: T)
}

class SimpleContainer : ServiceContainer, ServiceLocator {
    var locator: ServiceLocator { return self }
    
    private var registry : [String: Any] = [:]
    
    func registerService<T>(service: T) {
        let key = "\(T.self)"
        registry[key] = service
    }
    
    func getService<T>() -> T {
        let key = "\(T.self)"
        return registry[key] as! T
    }
}

let serviceContainer = SimpleContainer() as ServiceContainer

serviceContainer.registerService(Smokey() as Cat)
serviceContainer.registerService(Buddy() as Dog)

let client = Client(locator: serviceContainer.locator)

client.makeNoise() // "Cat goes Meeooow, dog goes Woof"