New class variables come into existence as soon as you use them!

Hmmm… for example:

class B {
  public function __construct($input) {
    $this->input = $input;
  }
  public function show() {
    print("input: $this->input\n");
  }
}

$b = new B(20);
$b->show();

will print 20, even though we never declared the class variable input in the class B.