Memento Pattern Generator

Creates Memento pattern infrastructure for capturing and restoring object state without violating encapsulation.

When to Use

Component Characteristics

Originator

• Creates memento from current state
• Restores state from memento
• Owns the state being saved
• Knows what to save/restore

Memento

• Stores originator’s internal state
• Immutable snapshot (readonly)
• Protects against external access
• Returns state only to originator

Caretaker

• Manages memento history
• Requests state saves
• Triggers state restoration
• Never examines memento contents

Generation Process

Step 1: Generate Memento

Path: src/Domain/{BoundedContext}/Memento/

1. {Name}Memento.php — Immutable state snapshot

Step 2: Generate Originator

Path: src/Domain/{BoundedContext}/

1. {Name}.php — Object with createMemento() and restore() methods

Step 3: Generate Caretaker

Path: src/Application/{BoundedContext}/

1. {Name}History.php — Manages memento stack for undo/redo

Step 4: Generate Value Objects (Optional)

Path: src/Domain/{BoundedContext}/ValueObject/

1. {State}.php — State representation value object

Step 5: Generate Tests

1. {Name}MementoTest.php — Memento creation tests
2. {Name}HistoryTest.php — Caretaker undo/redo tests

File Placement

Naming Conventions

Quick Template Reference

Memento

final readonly class {Name}Memento
{
    public function __construct(
        private {StateType} $state,
        private \DateTimeImmutable $createdAt
    ) {}

    public function state(): {StateType}
    {
        return $this->state;
    }

    public function createdAt(): \DateTimeImmutable
    {
        return $this->createdAt;
    }
}

Originator

final class {Name}
{
    private {StateType} $state;

    public function createMemento(): {Name}Memento
    {
        return new {Name}Memento(
            state: $this->state,
            createdAt: new \DateTimeImmutable()
        );
    }

    public function restore({Name}Memento $memento): void
    {
        $this->state = $memento->state();
    }
}

Caretaker

final class {Name}History
{
    private array $mementos = [];
    private int $currentIndex = -1;

    public function save({Name}Memento $memento): void
    {
        $this->mementos = array_slice($this->mementos, 0, $this->currentIndex + 1);
        $this->mementos[] = $memento;
        ++$this->currentIndex;
    }

    public function undo(): ?{Name}Memento
    {
        if ($this->currentIndex > 0) {
            --$this->currentIndex;
            return $this->mementos[$this->currentIndex];
        }
        return null;
    }

    public function redo(): ?{Name}Memento
    {
        if ($this->currentIndex < count($this->mementos) - 1) {
            ++$this->currentIndex;
            return $this->mementos[$this->currentIndex];
        }
        return null;
    }
}

Usage Example

// Create originator
$document = new Document(content: 'Initial text');

// Create caretaker
$history = new DocumentHistory();

// Save initial state
$history->save($document->createMemento());

// Make changes
$document->setContent('Modified text');
$history->save($document->createMemento());

$document->setContent('Final text');
$history->save($document->createMemento());

// Undo changes
$memento = $history->undo();
if ($memento) {
    $document->restore($memento); // Back to 'Modified text'
}

// Redo changes
$memento = $history->redo();
if ($memento) {
    $document->restore($memento); // Forward to 'Final text'
}

Common Memento Examples

Anti-patterns to Avoid

References

For complete PHP templates and examples, see:

• references/templates.md — Memento, Originator, Caretaker templates
• references/examples.md — Document, Order, Form state management with tests