What is the role of the Memento design pattern and when is it appropriate to use?

The Memento design pattern is a behavioral design pattern that allows an object to capture and externalize its internal state so that it can be restored later without violating encapsulation. It is used to provide the ability to undo or rollback an object's state to a previous state.

The primary role of the Memento pattern is to provide a mechanism for capturing and storing the internal state of an object, known as the originator, without exposing its implementation details. This captured state is then stored in a separate object called the memento. The originator can later restore its state from the memento object when needed.

The Memento pattern is appropriate to use in situations where there is a need to save and restore an object's state, especially when the object's state changes frequently and needs to be rolled back to a previous state. It is commonly used in applications that require undo/redo functionality, such as text editors, graphic design tools, or any application where the user can perform actions that need to be reversible.

By using the Memento pattern, the originator object can easily save its state to a memento object and store it in a caretaker object. The caretaker object acts as a caretaker of the mementos and provides an interface for managing and retrieving mementos. This separation of concerns allows the originator to focus on its core functionality while delegating the responsibility of managing the state to the caretaker.

Furthermore, the Memento pattern promotes encapsulation by ensuring that the originator's internal state is not directly accessible to other objects. This helps maintain the integrity of the object's state and prevents unauthorized modifications.

In summary, the Memento design pattern plays a crucial role in providing the ability to save and restore an object's state without violating encapsulation. It is appropriate to use when there is a need for undo/redo functionality or when frequent state changes need to be rolled back to a previous state.