OuterIterator
OuterIterator is a PHP interface that extends Iterator to represent iterators that wrap other iterators. It adds a single method, getInnerIterator(), which returns the inner iterator being wrapped.
OuterIterator is the foundation of PHP’s iterator decoration pattern: classes such as IteratorIterator, FilterIterator, MapIterator, LimitIterator, and RecursiveIteratorIterator all implement it.
Implementing OuterIterator allows building custom iterator decorators that add behaviour, such as filtering, mapping, or limiting, on top of any existing Traversable without modifying the wrapped object.
<?php
class DoubleValueIterator extends IteratorIterator implements OuterIterator
{
public function current(): mixed
{
return parent::current() * 2;
}
}
$array = new ArrayIterator([1, 2, 3, 4]);
$doubled = new DoubleValueIterator($array);
foreach ($doubled as $value) {
echo $value . PHP_EOL; // 2, 4, 6, 8
}
?>