访问PHP中父类中声明的对象

Question

Edit: Original example removed as it was complex.

The codes provided below doesn't work. I am trying to access the methods defined in a class which is declared in the parent class.

Here is a sample code. Its not working and I'd like to know why

<?php
function & get_instance()
{
    return Main::get_instance();
}


class Db{

    function select($var)
    {
        echo $var; 
    }
}

class Main
{
    public $db ;
    public $process ;
    private static $instance;

    function __construct()
    {
        self::$instance = &$this;

        $this->db = new Db ; 
        $this->process = Process; 

    }

    public static function & get_instance()
    {
        return self::$instance;
    }

}


class Process{

private $main ; 
    function __construct()
    {
        $this->main = get_instance() ; 
    }

    function processPayment()
    {
        $this->main->db->select("hello");
    }
}




$main = new Main ;

$main->process->processPayment(); 

Answer 1

To access members of a parent class, you will have to declare those members protected or public.

For example:

public var $db; 
protected var $orders;