tree-generators-php7.php

<?php

class Item
{
    public $name;
    public $parent;
    public function __construct($name, Item $parent = null)
    {
        $this->name = $name;
        $this->parent = $parent;
    }
}

function render(Item $item)
{
    yield $item;
    
    if ($item->parent)
        yield from render($item->parent);    
}

$a = new Item('a');
$b = new Item('b', $a);
$c = new Item('c', $b);
$d = new Item('d', $c);
$e = new Item('e', $d);

foreach (render($e) as $item) {
    echo $item->name . PHP_EOL;
}