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Date: Wed, 24 Aug 2005 14:45:43 -0700
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To: internals <internals@lists.php.net>
CC: Stanislav Malyshev <stas@zend.com>
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Subject: Schroedinger Objects
From: rasmus@lerdorf.com (Rasmus Lerdorf)

As per bug #34199 and as Rob points out, if($obj) and if(!$obj) are
handled by different opcodes and these two opcodes are inconsistent in
whether they call an object's cast_object handler.

if($obj) results in a ZEND_JMPZ_SPEC_CV_HANDLER which calls
i_zend_is_true() which always return true for objects, no matter what
(ignore compatibility mode here) because of this code in zend_execute.h:

        case IS_OBJECT:
            if(IS_ZEND_STD_OBJECT(*op)) {
                TSRMLS_FETCH();
                if(EG(ze1_compatibility_mode)) {
                    result = (zend_hash_num_elements(Z_OBJPROP_P(op))?1:0);
                } else {
                    result = 1;
                }
            } else {
                result = 1;
            }
            break;

if(!$obj) results in a which calls convert_to_boolean() which in turn
calls convert_object_to_type() which has:

if (Z_OBJ_HT_P(op)->cast_object) {

    if (Z_OBJ_HT_P(op)->cast_object(op, op, ctype, 1 TSRMLS_CC) ==
SUCCESS) {
         op->type = ctype;

    }

This means that any object which actually implements a cast_object
handler that returns false under some condition will be broken.  The
simple example is:

  $a = simplexml_load_string('<a></a>');
  if($a && !$a) echo "BUG!";

I think we need to fix i_zend_is_true's IS_OBJECT case to check to see
if the object has a cast_object handler and call it or just call
convert_to_boolean() there.  Or we need to clean this up and not have
such different codepaths for these two cases.

-Rasmus