Laracasts Iterator Lesson Examples: https://laracasts.com/series/how-do-i/episodes/3

Collection-Iterator-Aggregate.php

<?php

class Collection implements IteratorAggregate
{
    /**
     * The collection contents.
     *
     * @var array
     */
    protected $items;

    /**
     * Create a new counter instance.
     *
     * @param array $items
     */
    public function __construct($items = [])
    {
        $this->items = $items;
    }

    /**
     * Retrieve the iterator.
     *
     * @return ArrayIterator
     */
    public function getIterator()
    {
        return new ArrayIterator($this->items);
    }
}

// Usage:
$collection = new Collection(['a', 'b', 'c']);

foreach ($collection as $item) {
    var_dump($item);
}

Collection-Iterator.php

<?php

class Collection implements Iterator
{
    /**
     * The collection contents.
     *
     * @var array
     */
    protected $items;

    /**
     * Create a new counter instance.
     *
     * @param array $items
     */
    public function __construct($items = [])
    {
        $this->items = $items;
    }

    /**
     * Fetch the current item.
     *
     * @return mixed
     */
    public function current()
    {
        return current($this->items);
    }

    /**
     * Get the key for the current item.
     *
     * @return mixed
     */
    public function key()
    {
        return key($this->items);
    }

    /**
     * Move the pointer to the next item.
     *
     * @return mixed
     */
    public function next()
    {
        return next($this->items);
    }

    /**
     * Rewind the pointer to the first item.
     *
     * @return integer
     */
    public function rewind()
    {
        return reset($this->items);
    }

    /**
     * Determine if there are more items to iterate over.
     *
     * @return boolean
     */
    public function valid()
    {
        return current($this->items);
    }
}

// Usage:
$collection = new Collection(['a', 'b', 'c']);

foreach ($collection as $item) {
    var_dump($item);
}

Simple-Counting-Iterator.php

<?php

class Counter implements Iterator
{
    /**
     * The initial count.
     *
     * @var integer
     */
    protected $start;

    /**
     * The count to end at.
     *
     * @var integer
     */
    protected $end;

    /**
     * The current count.
     *
     * @var integer
     */
    protected $current;

    /**
     * Create a new counter instance.
     *
     * @param integer $start
     * @param integer $end
     */
    public function __construct($start, $end)
    {
        $this->start = $start;
        $this->end = $end;
        $this->current = $start;
    }

    /**
     * Prepare a new counter.
     *
     * @param  integer $start
     * @param  integer $end
     * @return static
     */
    public static function start($start, $end)
    {
        return new static($start, $end);
    }

    /**
     * Fetch the current count.
     *
     * @return integer
     */
    public function current()
    {
        return $this->current;
    }

    /**
     * Get the key for the current item.
     *
     * @return integer
     */
    public function key()
    {
        return $this->current;
    }

    /**
     * Move the pointer to the next item.
     *
     * @return integer
     */
    public function next()
    {
        return $this->current++;
    }

    /**
     * Rewind the pointer to the first item.
     *
     * @return integer
     */
    public function rewind()
    {
        return $this->current = $this->start;
    }

    /**
     * Determine if there are more items to iterate over.
     *
     * @return boolean
     */
    public function valid()
    {
        return $this->current <= $this->end;
    }
}

// Usage:
// Or: range(1, 10) :)
foreach (Counter::start(1, 10) as $number) {
    var_dump($number);
}