<?php

$tree = [
    'level1' => [
        'val1',
        'val2',
        'val3',
        'level2' => [
            'val4',
            'val5',
        ],
    ],
];

$iterator = new RecursiveTreeIterator(
    new RecursiveArrayIterator($tree)
);

$iterator->setPrefixPart(RecursiveTreeIterator::PREFIX_LEFT, ' ');
$iterator->setPrefixPart(RecursiveTreeIterator::PREFIX_MID_HAS_NEXT, '');
$iterator->setPrefixPart(RecursiveTreeIterator::PREFIX_MID_LAST, '|');
$iterator->setPrefixPart(RecursiveTreeIterator::PREFIX_END_HAS_NEXT, '-');
$iterator->setPrefixPart(RecursiveTreeIterator::PREFIX_END_LAST, '\\');
$iterator->setPrefixPart(RecursiveTreeIterator::PREFIX_RIGHT, ' ');

echo '<pre>';
foreach ($iterator as $val) {
    echo $val . PHP_EOL;
}
echo '</pre>';

 \ Array
 |- val1
 |- val2
 |- val3
 |\ Array
 ||- val4
 ||\ val5

• Using Closures in OOP
• Filtering elements of an Iterator
• Anonymous classes in PHP 7

PHP 8.2, Laminas MVC 3.2, Symfony 5.2, Laravel 8.28, PHPUnit 9.5, Doctrine ORM 2.8