readonly کردن یک پروپرتی داخل کلاس

 
//main class
class main
{
    private $_var = array();
    private $readonlyParams = array();
    
    protected function setReadOnlyParams($key=null)
    {
        if($key)
            $this->readonlyParams[] = $key;
    }
    
    public function __set($key,$val)
    {
        if( ! in_array($key,$this->readonlyParams))
            $this->_var[$key] = $val;
    }
    
    public function __get($key)
    {
        return isset($this->_var[$key])?$this->_var[$key]:null;
    }
    
    protected function setVar($key,$val)
    {
        $this->_var[$key] = $val;
    }
}
 
 
//child class
 
class child extends main
{
    
    public function __construct()
    {
        parent::setVar('param1','1');
        parent::setReadOnlyParams('param1');
        parent::setVar('param2','2');
    }
}
 
//example
 
$obj = new child;
echo $obj->param1; // show: 1
echo "<br>";
echo $obj->param2; // show: 2
 
echo "<hr>";
 
$obj->param1 = 'new 1';
$obj->param2 = 'new 2';
 
echo $obj->param1; // (read only params!)show:1 
echo "<br>";
echo $obj->param2; // show: new 2