<?php

class Base
{
    protected $_availableSizes = array();

    public function __call($name, $args)
    {
        $action = strtolower(substr($name, 0, 3));
        $field = '_' . strtolower($name[3]) . substr($name, 4);

        switch ($action) {
            case 'set':
                $this->$field = $args[0];
                break;

            case 'get':
                return $this->$field;
                break;

            default:
                break;
        }
    }
}

class Foo extends Base
{
    /**
     * Overrides the admin setAvailableSizes to ensure every
     * item within the context of an Order has a size and cost.
     *
     * @return void
     **/
    public function setAvailableSizes(array $sizes)
    {
        parent::setAvailableSizes($sizes);
        if (empty($this->_availableSizes)) {
            $this->_availableSizes[] = array(
                'name' => 'Default',
                'cost' => 0.00,
            );
        }
    }
}

$foo = new Foo();
$foo->setAvailableSizes(array(
    array(
        'name' => 'Test',
        'cost' => '0.00',
    ),
));

var_dump($foo);