PHP Recursive Iterator leaves

Question

I'm trying to get better understanding of iterators in PHP. For this test I wanted to make a tree of items, and list them with different RecursiveIteratorIterator modes. ::SELF_FIRST and ::CHILD_FIRST modes are working as I expect them to. However, it doesn't when I want to list leaves. There must be something I'm missing in implementation which doesn't allow that mode to work properly as it prints out nothing. Is there something wrong with my Obj::hasChildren() method?

Here is the test class:

class Obj implements \RecursiveIterator {
    public $children = array();

    private $position;

    private $name;

    public function __construct($name)
    {
        $this->name = $name;
    }

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

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

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

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

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

    public function hasChildren()
    {
        return !empty($this->children[$this->position]);
    }

    public function getChildren()
    {
        return $this->children[$this->position];
    }

    public function __toString()
    {
        return $this->name;
    }
}

And here is the test:

use RecursiveIteratorIterator as RII;

$o1 = new Obj('Root');

$i1 = new Obj('Item 1');
$i12 = new Obj('Subitem 2');
$i1->children[] = new Obj('Subitem 1');
$i1->children[] = $i12;

$i12->children[] = new Obj('Subsubitem 1');
$i12->children[] = new Obj('Enough....');

$o1->children[] = $i1;
$o1->children[] = new Obj('Item 2');
$o1->children[] = new Obj('Item 3');

foreach (new RII($o1, RII::LEAVES_ONLY) as $o) {
    echo "<br>" . $o;
}

Answer 1

What you assume is pointing in the right direction, there is a problem with the hasChildren() method you have. Compare it with the valid() and with the current() method, you then probably already see that it will always return true.

Because as long as there is a current(), hasChildren() returns true:

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

and:

public function hasChildren()
{
    return !empty($this->children[$this->position]);
}

Instead you want to test if the current element has children or not:

public function hasChildren()
{
    return !empty($this->current()->children);
}

The slight difference that will give you your output:

Subitem 1
Subsubitem 1
Enough....
Item 2
Item 3

By always returning TRUE for hasChildren(), the RecursiveIteratorIterator is unable to detect any leaves. By concept of a tree, this is not possible but in a traversal process - as you demonstrated with your "bug" - clearly possible :)

See as well (if I may):

• How does RecursiveIteratorIterator work in PHP?