/** 
 * The Command abstraction. 
 * In this case the implementation must return a result, 
 * sometimes it only has side effects. 
 */
interface Validator 
{ 
    /** 
     * The method could have any parameters. 
     * @param mixed 
     * @return boolean 
     */
    public function isValid($value); 
} 

/** 
 * ConcreteCommand. 
 */
class MoreThanZeroValidator implements Validator 
{ 
    public function isValid($value) 
    { 
        return $value > 0; 
    } 
} 

/** 
 * ConcreteCommand. 
 */
class EvenValidator implements Validator 
{ 
    public function isValid($value) 
    { 
        return $value % 2 == 0; 
    } 
} 

/** 
 * The Invoker. An implementation could store more than one 
 * Validator if needed. 
 */
class ArrayProcessor 
{ 
    protected $_rule; 

    public function __construct (Validator $rule) 
    { 
        $this->_rule = $rule; 
    } 

    public function process(array $numbers) 
    { 
        foreach ($numbers as $n) { 
            if ($this->_rule->IsValid($n)) { 
                echo $n, "\n"; 
            } 
        } 
    } 
} 

// Client code 
$processor = new ArrayProcessor(new EvenValidator()); 
$processor->process(array(1, 20, 18, 5, 0, 31, 42));