php - Protecting stand-alone variables -

is possible protect defined variable overriding (changing value)? making system uses plugins , want prevent plugin writer (myself) changing of specific defined variables (objects holds new class instances).

something this:

class foo {    function __construct() {     return "hello";   } } $bar= new foo(); 

so later, using global $bar; in functions don't want allow changing variable this:

$bar = new foo(); $bar = "new value";

$bar must stay same (new foo()) since going big system , cannot remember hundreds of core variables defined.

ideally be, if try redefine - php should throw fatal error. there such thing?

this sounds singleton pattern:

class foo {     protected static $instance = null;     protected function __construct()     {         throw new exception('use ::getinstance()');     }       public static function getinstance()     {         if (!isset(static::$instance)) {             static::$instance = new static;         }         return static::$instance;     } } 

use:

$bar = foo::getinstance(); 

any 1 can redeclare $bar .. if wont real foo ... need instance;