Building a tree from plain strings

tree.php

<?php
error_reporting(E_ALL);
ini_set("display_errors", 1);


class tree_item {
  public $title = '';
	public $children = array();

	public function &has_child($title) {
		foreach ($this->children as $c) {
			if ($c->title == $title) {
				return $c;
			}
		}
		return null;
	}

}


$nodes = array();

$in = array(
	'uno.due.tre.quattro',
	'uno.due.otto.nove'
	//'uno.cinque.sei.sette',
);


$root = new tree_item();
$root->title = 'uno';

foreach ($in as $item) {
	$data = explode(".", $item);

	$cur = &$root;

	foreach ($data as $idx => $d) {
		if ($idx == 0 && $root->title != $d)
			throw new Exception("root node must be unique");

		if ($idx > 0) {
			$node = &$cur->has_child($d);
			if ($node == null) {
				$tmp = new tree_item();
				$tmp->title = $d;
				$cur->children[] = $tmp;
				$size = count($cur->children);
				$cur =&$cur->children[$size-1];
			} else {
				$cur = &$node;
			}
		}
	}
}

print_r($root);