iterator-test.php

<pre>
<?php

require_once('iterator.class.php');

class MyIterator extends BaseIterator
{
	protected function getNextValue()
	{
//		var_dump(__METHOD__);
		static $count = 0;
		if (++$count % 5 == 0)
		{
			return null;
		}
		return $count;
	}
}

$i = new MyIterator();
var_dump($i);

for ($j = 0; $j < 3; $j++)
{
	foreach ($i as $v)
	{
		var_dump($v);
	}
	echo '[6] : ';
	var_dump($i[6]);
}

/**
 * This should print something like this:
string(20) "BaseIterator::rewind"
int(1)
int(2)
int(3)
int(4)
[6] : int(8)
string(20) "BaseIterator::rewind"
int(1)
int(2)
int(3)
int(4)
int(6)
int(7)
int(8)
int(9)
[6] : int(8)
string(20) "BaseIterator::rewind"
int(1)
int(2)
int(3)
int(4)
int(6)
int(7)
int(8)
int(9)
int(11)
int(12)
int(13)
int(14)
[6] : int(8)
*/

iterator.class.php

<?php

abstract class BaseIterator implements Iterator, ArrayAccess
{
	private $position = 0;
	private $cache = array();

	public function __construct()
	{
	}

	protected abstract function getNextValue();

	private function exists($position)
	{
		//var_dump(__METHOD__);
		return isset($this->cache[$position]);
	}

	private function updateCache($position)
	{
//		var_dump(__METHOD__);
//		var_dump($this->cache, $this->position);
		while (count($this->cache) <= $position)
		{
			$next = $this->getNextValue();
			if ($next === null)
			{
				return;
			}
			$this->cache[] =  $next;
		}
	}

	private function ensureCacheTo($position)
	{
//		var_dump(__METHOD__);
		if (!$this->exists($position))
		{
			$this->updateCache($position);
		}
	}

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

	public function current()
	{
//		var_dump(__METHOD__);
		$this->ensureCacheTo($this->position);
		return $this->cache[$this->position];
	}

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

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

	public function valid()
	{
		$this->ensureCacheTo($this->position);
		$exists = $this->exists($this->position);
		return $exists;
	}

	private function validateOffset($offset)
	{
		return is_int($offset);
	}

	public function offsetSet($offset, $value)
	{
		// TODO: handle setting?
		trigger_error('Cannot modify.', E_USER_WARNING);
	}

	public function offsetExists($offset)
	{
		if (!$this->validateOffset($offset))
		{
			return false;
		}
		$this->ensureCacheTo($offset);
		return isset($this->cache[$offset]);
	}

	public function offsetUnset($offset)
	{
		$this->offsetSet($offset, null);
	}

	public function offsetGet($offset)
	{
		if ($this->offsetExists($offset))
		{
			return $this->cache[$offset];
		}
		return null;
	}
}