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Questions and Answers
What design pattern can be used to avoid exposing internal details of classes while implementing the 'undo' feature?
Which design pattern would allow for the creation of a snapshot class that can store the state of the editor without exposing its internal details?
What is the main drawback of making the fields of the snapshot class public?
What is the main goal of implementing the 'undo' feature using design patterns?
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What is the consequence of restricting access to the state of the editor?
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What is the main issue with the direct approach to producing snapshots of an object's state?
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What would be the consequence of refactoring the editor classes in the future?
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What is the main benefit of using the Memento pattern?
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What type of data does a snapshot of the editor's state contain at a minimum?
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What is the alternative to the direct approach to producing snapshots of an object's state?
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What is the main issue with the Memento pattern?
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What is the role of the classes responsible for copying the state of the affected objects?
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What is the name of the pattern that lets you save and restore the previous state of an object?
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Study Notes
Memento Design Pattern
- The Memento pattern allows saving and restoring an object's previous state without exposing its implementation details.
Problem with Implementation
- Creating a text editor app with undo feature by recording the state of all objects and saving it in storage before performing any operation.
- The approach requires going over all the fields in an object and copying their values into storage.
- However, this approach has issues:
- Most real objects won't allow access to their private fields.
- Refactoring classes or adding/removing fields would require changing the classes responsible for copying the state.
Snapshot Issues
- A snapshot of the editor's state would contain data such as text, cursor coordinates, and scroll position.
- To make a snapshot, one needs to collect these values and put them into a container, likely a class with many fields and few methods.
- The container class would need to have public fields to allow other objects to write and read data, exposing all the editor's states.
The Dilemma
- Either expose all internal details of classes, making them fragile, or restrict access to their state, making it impossible to produce snapshots.
- There should be another way to implement the "undo" feature without these drawbacks.
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Description
Learn how the Memento pattern enables undo functionality in text editing applications. Understand how it saves and restores object states without revealing implementation details.
