NSKeyedArchiver using Swift 4 Codable protocol

ProductCodable.swift

struct Product: Codable {
  var title: String
  var price: Double
  var quantity: Int
  
  init(title: String, price: Double, quantity: Int) {
    self.title = title
    self.price = price
    self.quantity = quantity
  }
}

// Store an Array of products

func storeProducts() {
  do {
    let data = try PropertyListEncoder().encode(products)
    let success = NSKeyedArchiver.archiveRootObject(data, toFile: productsFile.path)
    print(success ? "Successful save" : "Save Failed")
  } catch {
    print("Save Failed")
  }
}

// Retrieve an Array of products

func retrieveProducts() -> [Product]? {
  guard let data = NSKeyedUnarchiver.unarchiveObject(withFile: productsFile.path) as? Data else { return nil }
  do {
    let products = try PropertyListDecoder().decode([Product].self, from: data)
    return products
  } catch {
    print("Retrieve Failed")
    return nil
  }
}

// Source: https://medium.com/if-let-swift-programming/migrating-to-codable-from-nscoding-ddc2585f28a4

// Full implementation

struct Product: Codable {
  
  var title:String
  var price:Double
  var quantity:Int
  
  enum CodingKeys: String, CodingKey {
    case title
    case price
    case quantity
  }
  
  init(title:String,price:Double, quantity:Int) {
    self.title = title
    self.price = price
    self.quantity = quantity
  }
  
  func encode(to encoder: Encoder) throws {
    var container = encoder.container(keyedBy: CodingKeys.self)
    try container.encode(title, forKey: .title)
    try container.encode(price, forKey: .price)
    try container.encode(quantity, forKey: .quantity)
  }
  
  init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    title = try container.decode(String.self, forKey: .title)
    price = try container.decode(Double.self, forKey: .price)
    quantity = try container.decode(Int.self, forKey: .quantity)
  }
}

what is PropertyListEncoder and PropertyListDecoder ??