#38866 [Opn->Fbk]: Nesting level too deep Error when Object Contains Self Reference

From: Date: Mon, 18 Sep 2006 15:35:45 +0000
Subject: #38866 [Opn->Fbk]: Nesting level too deep Error when Object Contains Self Reference
References: 1  Groups: php.bugs 
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 ID:               38866
 Updated by:       tony2001@php.net
 Reported By:      adam at sccode dot com
-Status:           Open
+Status:           Feedback
 Bug Type:         Class/Object related
 Operating System: Windows 2000
 PHP Version:      5CVS-2006-09-18 (snap)
 New Comment:

After this change I get only bool(false).
What is the problem?


Previous Comments:
------------------------------------------------------------------------

[2006-09-18 15:21:14] adam at sccode dot com

Apologies ... I posted the wrong reproduce code:

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

Should read:

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

In previous versions of PHP this has produced no error. There are
sometimes occasions where checking if two varaibles reference the same
object instance is necessaary - I don't think a static property should
break this.

------------------------------------------------------------------------

[2006-09-18 15:11:04] tony2001@php.net

With $this->attr = $this you get recursive references, so the error
message is expected.

------------------------------------------------------------------------

[2006-09-18 14:37:19] adam at sccode dot com

Description:
------------
Attempting to compare two variables containing a reference to an object
instance which in turn contains a property static or otherwise,
referring back to itself produces a "Nesting level too deep" fatal
error. One example where a self references may be necessary is a
singleton: in PHP 5.1.6 the reproduce code works as expected. A
feature, or a bug?

Reproduce code:
---------------
    $obj = Singleton::instance();
    $obj2 = $obj;

    var_dump($obj != $obj2);

    class Singleton
    {
        private static $instance;
        
        private function __construct()
        {
            $this->me = $this;
        }

        public static function instance()
        {
            if (! self::$instance) {
                self::$instance = new Singleton;
            }

            return self::$instance;
        }
    }

Expected result:
----------------
bool(false)

Actual result:
--------------
Fatal error: Nesting level too deep - recursive dependency? in
crash-test.php on line 5


------------------------------------------------------------------------


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