LH17

protocol Country {
    func accept(visitor: CountryVisitor)
}

protocol CountryVisitor {
    func visit(country: India)
    func visit(country: Brazil)
    func visit(country: China)
}

LH17

protocol Office {
    func officeSchedule()
}

protocol Employee {
    func work()
    func getPaid()
}

LH17

protocol Strategy {
    func convert(number: Int)
}

class Convert {
    var strategy: Strategy
    var number: Int
    
    init(number: Int, strategy: Strategy) {

LH17

protocol Human {
    // MARK: - Getter
    func getState() -> ManState
    // MARK: - Setter
    func set(state: ManState)
}

protocol ManState {
    func stand()

LH17

protocol Observable {
    func add(customer: Observer)
    func remove(customer : Observer)
    func notify()
}

protocol Observer {
    var id: Int { get set }
    func update()

LH17

import UIKit

typealias MementoType = [String: Any]

protocol Memento: class {
    var key: String  { get set }
    var state: MementoType { get set }
    
    func save()

LH17

protocol Receiver {
    var name: String { get }
    func receive(message: String)
}

protocol Sender {
    var teams: [Receiver] { get set }
    func send(message: String, sender: Receiver)
}

LH17

struct MyBestFilms: Sequence {
    let films: [String]
    
    func makeIterator() -> MyBestFilmsIterator {
        return MyBestFilmsIterator(films)
    }
}

struct MyBestFilmsIterator: IteratorProtocol {

LH17

protocol Command {
    func execute()
}

class ConcreteCommand: Command {
    var colorReceiver: ColorReceiver
    
    init(colorReceiver: ColorReceiver) {
        self.colorReceiver = colorReceiver

LH17

enum Level: Int {
    case state = 1
    case national = 2
    case international = 3
}

class Sports {
    var level: Level