PHP pattern "strategy" example, with ducks

strategy.php

// from "Head First Design Patterns by Eric Freeman"

interface FlyBehavior 
{
  public function fly();
}

class FlyWithWings implements FlyBehavior
{
  public function fly() {
    echo 'i`m flying', PHP_EOL;
  }
}

class FlyNoWay implements FlyBehavior
{
  public function fly() {
    echo 'i can`t fly', PHP_EOL;
  }
}

// base class
class Duck 
{
  public $flyBehavior;
  
  public function performFly() {
    $this->flyBehavior->fly();
  }
  
  public function setFlyBehavior($fb) {
    $this->flyBehavior = $fb;
  }
  
  public function swim() {
    echo 'i swim', PHP_EOL;
  }  
}

class MallardDuck extends Duck
{
  public function __construct() {
    $this->flyBehavior = new FlyWithWings();
  }
}

class RubberDuck extends Duck 
{
  public function __construct() {
    $this->flyBehavior = new FlyNoWay();
  }
}

// check it
echo 'i`m mallard duck', PHP_EOL;
$mallard = new MallardDuck();
$mallard->performFly();
$mallard->swim();

echo PHP_EOL;
echo 'i`m rubber duck', PHP_EOL;
$rubber = new RubberDuck();
$rubber->performFly();
$rubber->swim();

// dynamic behavior change 
echo PHP_EOL;
$mallard2 = new MallardDuck();
$mallard2->performFly();
$mallard2->setFlyBehavior(new FlyNoWay);
$mallard2->performFly();