# Memento Pattern

> A design pattern in which an object captures its own state in an opaque snapshot it can later restore.

Record: `architecture:memento-pattern`
Kind: pattern
Layer: [Design Patterns Core](https://banes-lab.com/records/layer/design-patterns-core.md)
Severity: contextual
Scope: behavior, state capture, history
Canonical: https://banes-lab.com/ontology#architecture-memento-pattern

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Visitor Pattern](https://banes-lab.com/records/architecture/visitor-pattern.md) and before [Null Object Pattern](https://banes-lab.com/records/architecture/null-object-pattern.md).

## Repair

- Refactored by: Capture State as a Memento
- Detected by: external code reconstructing internal state
- Violated by: callers copying an object's private fields to save state
- Measured by: private-field external access count
- Enforced by: [design review](https://banes-lab.com/records/architecture/design-review.md)

## Requires

- [Encapsulation](https://banes-lab.com/records/architecture/encapsulation.md)

## Reinforces

- [Information Hiding](https://banes-lab.com/records/architecture/information-hiding.md)

## Enables

- [Undo/Redo](https://banes-lab.com/records/lexicon/undo-redo.md)
- [Snapshot/Restore](https://banes-lab.com/records/lexicon/snapshot-restore.md)

## Conflicts with

- [External State Reach-In](https://banes-lab.com/records/lexicon/external-state-reach-in.md)

## In tension with

- [Memory Footprint](https://banes-lab.com/records/lexicon/memory-footprint.md)

## Tensions

- [Memento Pattern / Memory Footprint](https://banes-lab.com/records/tension/memento-pattern-memory-footprint.md)

## Severity

- [contextual](https://banes-lab.com/records/vocabulary/severity-contextual.md)

## Category

- [Behavioral Patterns](https://banes-lab.com/records/architecture-category/behavioral-patterns.md)

## Enforced by

- [rules/eslint/require-snapshot-coverage.eslint.rule.ts](https://banes-lab.com/source/governance/rules/eslint/require-snapshot-coverage.eslint.rule.ts.md)

## Linked from

- [Execution joins the halves](https://banes-lab.com/software-architecture/principles/execution-joins-the-halves.md)
- [Core Modular Design](https://banes-lab.com/ontology/principles/architecture-category-core-modular-design.md)
- [Behavioral Patterns](https://banes-lab.com/ontology/lexicon/lexicon-category-behavioral-patterns.md)
- [Core Vocabulary](https://banes-lab.com/ontology/lexicon/lexicon-category-core-vocabulary.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)