php

a.php

<?php
	
	// Friend and property support
	
	// Read-only properties
		abstract class PropertyVars {
			protected $__visible = array();
			public function &__get($key) {
				if(in_array($key, $this->__visible)) {
					return $this->$key;
				}

				// normal __get() code here
				trigger_error('Cannot access private property ' . __CLASS__ .'::$'.$key, E_USER_ERROR);
			}
		}
?>