Memento Pattern

Captures and externally stores an object's internal state so it can be restored later — enabling undo/redo without exposing private implementation details.

#behavioral#memento#undo#snapshot#encapsulation#gof

Field Note - Real-world Analogy

Think of it like this

“Like a time capsule. A person (Originator) writes a letter about their current life and seals it in a capsule (Memento). A librarian (Caretaker) stores the sealed capsule and can retrieve it later — but never opens or reads it. When the person wants to remember their past self, they open their own capsule. Nobody else can read it, preserving privacy (encapsulation).”

Field Observations - Key Topics Covered

The problem: you want to implement undo for a text editor. The naive approach is to save a copy of the entire editor state somewhere. But if you just expose the editor's internal fields (cursor position, text content, formatting) to the outside class that manages history, you've broken encapsulation — external code now knows about and depends on internal details.

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