silverstripe-fulltextsearch/code/utils/MultipleArrayIterator.php

<?php

class MultipleArrayIterator implements Iterator {

	protected $arrays;
	protected $active;

	function __construct() {
		$args = func_get_args();

		$this->arrays = array();
		foreach ($args as $arg) {
			if (is_array($arg) && count($arg)) $this->arrays[] = $arg;
		}

		$this->rewind();
	}

	function rewind() {
		$this->active = $this->arrays;
		if ($this->active) reset($this->active[0]);
	}

	function current() {
		return $this->active ? current($this->active[0]) : false;
	}

	function key() {
		return $this->active ? key($this->active[0]) : false;
	}

	function next() {
		if (!$this->active) return;

		if (next($this->active[0]) === false) {
			array_shift($this->active);
			if ($this->active) reset($this->active[0]);
		}
	}

	function valid() {
		return $this->active && (current($this->active[0]) !== false);
	}
}