Redefining PHP Classes

Hey there,

I have a class A that uses class B. Class B also uses class A. This is recursive and am wondering if you can redefine PHP classes like in C++.

class A{}

class B{
    private $classA;

    public function __construct($classA){
       $this->classA = $classA;
    }

    public function someFunc(){ echo 'blah'; }
}

class A{
    private $classB;

    public function __construct($classB){
        $classB->someFunc();
    }
}