Advanced PHP Interface Example: Traversable and Countable extended

advanced-interface-example.php

<?php
/**
 * Advanced PHP Interface Example: Traversable and Countable extended
 *
 * As Traversable is an internal interface but PHP interfaces allow to extend
 * from multiple interfaces, it is possible to create your own internal
 * type (here based on Traversable) and base another non-internal sub-type 
 * on it (here based on IteratorAggregate).
 *
 * @link http://wpkrauts.com/2013/how-to-build-flexible-php-interfaces/
 * @link https://eval.in/39494
 */

interface CountableTraversable 
    extends Traversable, Countable
{
}

interface CountableTraversableAggregate 
    extends CountableTraversable, IteratorAggregate
{
}

class Widgets implements CountableTraversableAggregate
{
    private $widgets = array('Blue', 'Red');
    
    function getIterator() 
    {
        return new ArrayIterator($this->widgets);
    }

    function count() 
    {
        return count($this->widgets);
    }
}

$widgets = new Widgets();

printf("You have %d widgets:\n", count($widgets));

foreach($widgets as $key => $widget) {
    printf("[%s]: %s\n", $key, $widget);
}

Another option to loop through the array would be to use the Iterator methods directly:

$widgets = ( new Widgets() )->getIterator();
$widgets->rewind();

printf( "You have %d widgets:\n", count( $widgets ) );

while( $widgets->valid() ) {
    printf ("[%d]: %s\n", $widgets->key(), $widgets->current() );
    $widgets->next();
}

which , in theory, should scale better memory wise with increasing size of the looped array. Also it's good habit to actually rewind() an Iterator before a loop as it could be stuck somewhere in the middle from a previous, interrupted loop.