LH17

protocol ViewStateProtocol: class {
    var stateManager: StateManager? { get }
    
    var loadingView: UIView? { get }
    var errorView: UIView? { get }
    var emptyView: UIView? { get }
    
    var errorMessage: String? { get set }
    func addView(withState state: StatesType)
}

LH17

extension ViewStateProtocol where Self: UIViewController {
    
    // State manager class to remove/add views
    var stateManager: StateManager? {
        return StateManager.sharedInstance
    }
    
    // Loading view
    var loadingView: UIView? {
        return LoadingView(frame: UIScreen.main.bounds)

LH17

extension ViewStateProtocol where Self: UIViewController {
    ..........
     // Manages and adds different views on the basis of the state
    func addView(withState state: StatesType) {
        
        // error state, empty state & loading state
        switch state {
        case .loading:
            // calls state manager to add a laoding view
            stateManager?.addView(loadingView!, forState: StatesType.loading.rawValue, superview: view)

LH17

enum StatesType: String {
    case error = "error"
    case empty = "empty"
    case loading = "loading"
    case none = "none"
}

LH17

class StateManager {
  
    static let sharedInstance = StateManager()
    var viewStore: [String: UIView] = [:]
    
    // Associates a view for the given state
    public func addView(_ view: UIView, forState state: String, superview: UIView) {
        viewStore[state] = view
        superview.addSubview(view)
    }

LH17

class StateViewController: UIViewController {}

extension StateViewController: ViewStateProtocol {
	@objc func handleTap(_ sender: UIView) {
		// for showing the loader
		addView(withState: .loading)

		// for showing the error message
		addView(withState: .error)

LH17

precedencegroup UnionOperatorPrecedence {
    associativity: left
}

infix operator ∪: UnionOperatorPrecedence

func ∪ <T:Equatable>(lhs: [T], rhs:[T])->[T] {
    var result = lhs
    for element in rhs {
        if !lhs.contains(element) {

LH17

precedencegroup IntersectionOperatorPrecedence {
    associativity: left
}

infix operator ∩: IntersectionOperatorPrecedence

func ∩<T: Equatable> (left: [T], right: [T]) -> [T] {
    var intersection: [T] = []
    for value in left {
        if right.contains(value) {

LH17

precedencegroup UnionOperatorPrecedence {
    associativity: left
    higherThan: IntersectionOperatorPrecedence
}

LH17

// Protocol
protocol Fruit {
    func set(price: String?)
    func clone() -> Fruit
}

// Class Apple which implements the protocol
class Apple: Fruit {
    var count: Int