Iterator Pattern Generator

Creates Iterator pattern infrastructure for sequential access to collection elements.

When to Use

Scenario	Example
Traverse collections	Order items, user lists, product catalog
Multiple traversal algorithms	Forward, backward, filtered iteration
Unified collection interface	Standardize iteration across different types
Hide collection structure	Encapsulate internal representation

Component Characteristics

Iterator Interface

• Extends \Iterator or \IteratorAggregate
• Provides current(), next(), key(), valid()
• Enables foreach compatibility
• Type-safe element access

Concrete Iterator

• Implements traversal algorithm
• Maintains iteration state
• Provides filtering/transformation
• Resets to beginning via rewind()

Iterable Collection

• Implements \IteratorAggregate
• Returns iterator via getIterator()
• Encapsulates collection data
• Supports type-safe operations

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Generation Process

Step 1: Generate Iterator Interface (Optional)

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

1. {Name}IteratorInterface.php — Custom iterator contract (extends \Iterator)

Step 2: Generate Concrete Iterator

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

1. {Name}Iterator.php — Iterator implementation with traversal logic
2. Filtered{Name}Iterator.php — Filtered variant (optional)

Step 3: Generate Iterable Collection

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

1. {Name}Collection.php — Collection implementing \IteratorAggregate

Step 4: Generate Value Objects (Optional)

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

1. {Element}.php — Collection element type

Step 5: Generate Tests

1. {Name}IteratorTest.php — Iterator behavior tests
2. {Name}CollectionTest.php — Collection tests

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File Placement

Component	Path
Iterator Interface	src/Domain/{BoundedContext}/Iterator/
Concrete Iterator	src/Domain/{BoundedContext}/Iterator/
Collection	src/Domain/{BoundedContext}/Collection/
Value Objects	src/Domain/{BoundedContext}/ValueObject/
Unit Tests	tests/Unit/Domain/{BoundedContext}/

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Naming Conventions

Component	Pattern	Example
Iterator Interface	{Name}IteratorInterface	OrderIteratorInterface
Concrete Iterator	{Name}Iterator	OrderIterator
Filtered Iterator	Filtered{Name}Iterator	FilteredUserIterator
Collection	{Name}Collection	OrderCollection
Test	{ClassName}Test	OrderIteratorTest

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Quick Template Reference

Iterator (using \Iterator)

final class {Name}Iterator implements \Iterator
{
    private int $position = 0;

    public function __construct(
        private readonly array $items
    ) {}

    public function current(): {ElementType}
    {
        return $this->items[$this->position];
    }

    public function next(): void
    {
        ++$this->position;
    }

    public function key(): int
    {
        return $this->position;
    }

    public function valid(): bool
    {
        return isset($this->items[$this->position]);
    }

    public function rewind(): void
    {
        $this->position = 0;
    }
}

Iterable Collection (using \IteratorAggregate)

final readonly class {Name}Collection implements \IteratorAggregate, \Countable
{
    /**
     * @param array<{ElementType}> $items
     */
    public function __construct(
        private array $items = []
    ) {}

    public function getIterator(): \Traversable
    {
        return new {Name}Iterator($this->items);
    }

    public function count(): int
    {
        return count($this->items);
    }
}

---

Usage Example

// Create collection
$orders = new OrderCollection([
    new Order(id: '1', total: 100),
    new Order(id: '2', total: 200),
    new Order(id: '3', total: 50),
]);

// Iterate with foreach
foreach ($orders as $order) {
    echo $order->total();
}

// Filtered iteration
$filtered = new FilteredOrderIterator(
    orders: $orders,
    filter: fn(Order $o) => $o->total() > 100
);

foreach ($filtered as $order) {
    // Only orders with total > 100
}

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Common Iterator Patterns

Domain	Iterators
Collections	OrderCollection, UserCollection, ProductCollection
Filtering	ActiveUserIterator, PendingOrderIterator
Pagination	PaginatedResultIterator, PageIterator
Tree Structures	DepthFirstIterator, BreadthFirstIterator
Composite	RecursiveIterator, FlatteningIterator

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
Mutable iterator state leak	External modification	Use readonly collections
Breaking foreach contract	Invalid implementation	Implement all \Iterator methods
Expensive current()	Performance issues	Cache current element
Missing rewind()	Can't iterate twice	Implement proper rewind()
Violating LSP	Inconsistent behavior	Follow SPL iterator contracts

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References

For complete PHP templates and examples, see:

• references/templates.md — Iterator, IteratorAggregate, Filtered Iterator templates
• references/examples.md — OrderCollection, UserIterator, Pagination with tests