Object-Oriented Programming: Beyond the Basics

Oct 17 2023 · Swift 5.9, iOS 17, Xcode 15

Lesson 05: Liskov Substitution, Interface Segregation & Dependency Inversion

Demo 1

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In this demo, you’ll put the Liskov Substitution to work. You’ll pick up right where you left off with the contacts app in the previous lesson.

public class EmergencyContactCard: ContactCard {
  override private init(firstName: String, lastName: String, phoneNumber: String) {
    super.init(firstName: firstName, lastName: lastName, phoneNumber: phoneNumber)
    canAdd = []
    cardType = .emergency
  }

 public convenience init?(emergencyName: String, phoneNumber: String) {
  if phoneNumber.count != 3 {
    return nil
  }
    self.init(firstName: emergencyName, lastName: "", phoneNumber: phoneNumber)
  }

 public override func contactInformation() -> String {
    "Contact: EmergencyName: \(firstName), Phone: \(phoneNumber)"
  }
}

public override func set(phone: String) {
  guard phone.count == 3 else {
    return
  }
  super.set(phone: phone)
}

public func set(firstName: String, lastName: String) -> Bool {
  self.firstName = firstName
  self.lastName = lastName
  broadcastUpdates()
  return true
}

public func set(phone: String) -> Bool {
  phoneNumber = phone
  broadcastUpdates()
  return true
}

public func set(phone: Double) -> Bool {
  phoneNumber = "\(phone)"
  broadcastUpdates()
  return true
}

public override func set(phone: String) -> Bool {
  guard phone.count == 3 else {
  return false
  }
  return super.set(phone: phone)
}

let emergencyContact1 = EmergencyContactCard(emergencyName: "Cold Store Creamery", phoneNumber: "555")

let emergencyContact2 = EmergencyContactCard(emergencyName: "Rifftrax", phoneNumber: "")

print("emergency 1: \(emergencyContact1?.contactInformation() ?? "None")")
print("emergency 21: \(emergencyContact2?.contactInformation() ?? "None")")
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