<?php

class controller {
    var $db;
    var $user;
    
    function init_db() {
        $this->db = new db();
        $this->db->host = 'localhost';
    }
    
    function init_user() {
        $this->user = new user($this);
    }
}

class db {
    var $host;
}

class user {
    var $controller;
    var $db;
    function __construct(&$controller) {
        $this->controller = $controller;
        $this->db = $controller->db;
    }
    
    function login() {
        var_dump($this->db);
    }
}


$controller = new controller();
$controller->init_user();
$controller->init_db();

$controller->user->login(); // Output NULL, Why not output localhost