Head first design pattern bug - php

Question

I am studying Head First - design patterns and translating the exercises to PHP.
I dont get any errors but there is a bug that I cannot figure out.
Edit ( Code ):
abstract class Cat
{
public $meowBehaviour, $eatBehaviour;
function __construct(MeowBehaviour $meowBehaviour, EatBehaviour $eatBehaviour)
{
$this->meowBehaviour = $meowBehaviour;
$this->eatBehaviour = $eatBehaviour;
}
public abstract function sits();
public function performMeowBehaviour()
{
$this->meowBehaviour->meow();
}
public function performEatBehaviour()
{
$this->eatBehaviour->eat();
}
}
interface EatBehaviour {
public function eat();
}
class EatCatFood implements EatBehaviour {
public function eat()
{
echo "I eat cat food. <br />";
}
}
class EatGazzelle implements EatBehaviour {
public function eat()
{
echo "I hunt and eat gazzelle. <br />";
}
}
interface MeowBehaviour {
public function meow();
}
class Meow implements MeowBehaviour {
public function meow()
{
echo "meow <br />";
}
}
class Roar implements MeowBehaviour {
public function meow()
{
echo "ROAR! <br />";
}
}
class HouseCat extends Cat
{
function __construct()
{
parent::__construct(new Meow, new EatCatFood);
}
public function sits()
{
echo "if I fits I sits";
}
}
class CatSimulator {
public $cat;
public function __construct()
{
$this->cat = new HouseCat;
$this->cat->performMeowBehaviour();
$this->cat->performEatBehaviour();
}
}
$c = new CatSimulator;
the output from CatSimulator is
meow
meow
I eat cat food.
I cannot figure out why 'meow' is repeated.

Answer 1

In PHP function names are case-insensitive. So here:
class Meow implements MeowBehaviour {
public function meow()
{
echo "meow <br />";
}
}
... meow() is treated as a constructor (PHP 4.x style) - and gets called on $this->cat = new HouseCat; line, echoing the first 'meow'.
You can rename the class, of course, but there's another alternative: add explicit constructor in that class, as here:
class Meow implements MeowBehaviour {
public function __construct() {}
public function meow()
{
echo "meow <br />";
}
}
Now meow method will be called only once.
It's important that __construct() precedes meow(), otherwise E_STRICT error will be raised. You can read more about it here.