Class works without declaring variables?

Question

I'm learned php as functional and procedure language. Right now try to start learn objective-oriented and got an important question.

I have code:

class car {

    function set_car($model) {
        $this->model = $model;
    }

    function check_model()
    {
        if($this->model == "Mercedes") echo "Good car";
    }

}

$mycar = new car;
$mycar->set_car("Mercedes");

echo $mycar->check_model();

Why it does work without declaration of $model?

var $model; in the begin?

Because in php works "auto-declaration" for any variables? I'm stuck

Answer 1

Every object in PHP can get members w/o declaring them:

$mycar = new car;
$mycar->model = "Mercedes";
echo $mycar->check_model(); # Good car

That's PHP's default behaviour. Those are public. See manual.

Answer 2

Yes, if it doesn't exist, PHP declares it on the fly for you.

It is more elegant to define it anyway, and when working with extends it's recommended, because you can get weird situations if your extends are gonna use the same varnames and also don't define it private, protected or public.

More info: http://www.php.net/manual/en/language.oop5.visibility.php