PHP5 实现只读、只写属性

<?php  
    class LoRuiDb
    {
        private $readonly = '<br>只读属性<br>';
        private $writeonly;
        private $readandwrite;
        
        function __get($n)
        {
            switch($n)
            {
                case 'ReadOnly':
                    return $this->readonly;
                    
                    break;
                case 'WriteOnly':
                    return 'WriteOnly属性只写，不能获取值！';
                    break;
                case 'ReadAndWrite':
                    return $this->readandwrite;
                    break;
            }
        }
        function __set($n,$v)
        {
            switch($n)
            {
                case 'ReadOnly':
                    echo 'ReadOnly属性只读，不能设置值！';
                    break;
                case 'WriteOnly':
                    $this->writeonly = $v;
                    
                    break;
                case 'ReadAndWrite':
                    $this->readandwrite = $v;
                    break;
            }
        }
        
        
        public function ShowWriteOnlyValue()
        {
            echo "<p>$this->writeonly</p>";
        }
        
        function __construct($msg='Default Msg')
        {
            echo $msg;
        }
        function __destruct()
        {
            echo 'bye LoRuiDb';
        }
    }
    
    $db = new LoRuiDb('龙睿·LoRui');
    echo $db->ReadOnly;
    $db->ReadOnly = 'php class';
    echo $db->ReadOnly;
    echo $db->WriteOnly;
    $db->WriteOnly = 'Acer 4315';
    $db->ShowWriteOnlyValue();
    $db->ReadAndWrite = 'Geany<br>';
    echo $db->ReadAndWrite;
?>