Designing with Swift: Utilizing the Memento Pattern

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Designing with Swift: Utilizing the Memento Pattern

Swift is an incredibly powerful programming language, allowing developers to create complex and sophisticated applications quickly. The Memento pattern is a design pattern that enables developers to save and restore object states. By utilizing this pattern, developers can easily save and restore complex states of their objects without having to write a lot of code. In this blog post, we will explore how to use the Memento pattern in Swift.

The Memento pattern is simple yet effective. It requires two parts: the memento, which stores the state of an object, and the caretaker, which is responsible for saving and restoring the state. To save the state of an object, simply call the memento’s save() method. This method will store the current state of the object in a data structure. To restore the state of an object, simply call the memento’s restore() method. This method will retrieve the stored state from the data structure and apply it to the object.

Let’s look at a simple example of the Memento pattern in Swift. We’ll create a class called Person, which has three properties – name, age, and height. We also create a class called PersonMemento, which stores the state of the Person class. 

class Person {
  var name: String
  var age: Int
  var height: Int
  init(name: String, age: Int, height: Int) {
    self.name = name
    self.age = age
    self.height = height
  }
}

class PersonMemento {
  var name: String
  var age: Int
  var height: Int
  init(person: Person) {
    self.name = person.name
    self.age = person.age
    self.height = person.height
  }
}

Now we can use the Memento pattern in our Person class. We can add two methods – save() and restore() – to our Person class. The save() method creates a new instance of the PersonMemento class and stores the current state of the Person object. The restore() method retrieves the stored state from the PersonMemento and applies it to the Person object. 

extension Person {
  func save() -> PersonMemento {
    return PersonMemento(person: self)
  }
  
  func restore(memento: PersonMemento) {
    self.name = memento.name
    self.age = memento.age
    self.height = memento.height
  }
}

Now we can use the save() and restore() methods to save and restore the state of our Person object. Let’s create a Person object and save its state: 

let person = Person(name: "John", age: 30, height: 180)
let memento = person.save()

Now we can change the state of our Person object and then restore it using the memento: 

person.name = "Jane"
person.age = 40
person.restore(memento: memento)

After restoring the state, the Person object will have the same state as when it was first saved.

The Memento pattern is a great tool for developers who need to save and restore complex states of their objects. By utilizing the Memento pattern, developers can easily save and restore states without having to write a lot of code. This makes it easy to add undo/redo functionality to their apps, or to save application state between launches. With the Memento pattern, developers can easily design sophisticated applications using Swift.

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