<?php
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
class A{
    protected static $instance = null;

    public static function getInstance(){
        if(self::$instance === null)
            self::$instance = new self();
        return self::$instance;
    }

    public function show($param){
        echo 'Show '.$param.chr(10);
    }

    public function __destruct(){
        echo 'Destruct '.__CLASS__.chr(10);
    }
}
class B extends Mysqli{
    public function __destruct(){
        A::getInstance()->show(__CLASS__);
        echo 'Destruct '.__CLASS__.chr(10);
    }
}
class C{
    protected static $class = null;

    public static function attachClass(&$class){
        self::$class = $class;
    }

    public function __destruct(){
        A::getInstance()->show(__CLASS__);
        echo 'Destruct '.__CLASS__.chr(10);
    }
}

$a = A::getInstance();
$b = new B();
$GLOBALS['d'] = $b;
// or
C::attachClass($b);
$c = new C();
?>