Bug #72194 [Opn]: unset() on declared class properties undeclares it partially

Edit report at https://bugs.php.net/bug.php?id=72194&edit=1 ID: 72194 Updated by: bwoebi@php.net Reported by: pierre dot rineau at makina-corpus dot com Summary: unset() on declared class properties undeclares it partially Status: Open Type: Bug Package: Reflection related Operating System: Any PHP Version: Irrelevant Block user comment: N Private report: N New Comment: The property (as in property declaration) still exists. Only dynamic properties can completely vanish. The correct construct checking for existence of the property *value* is isset(). Note that unset() sets the value to undefined [not null!], but does not affect the existence of the property declaration if it is a declared one. class A { public $b; } $a = new A; var_dump(property_exists($a, "b")); // true var_dump(isset($a->b)); // false (as $a->b is null) var_dump($a->b); // null var_dump(property_exists($a, "c")); // false $a->c = 1; var_dump(property_exists($a, "c")); // true unset($a->c); var_dump(property_exists($a, "c")); // false unset($a->b); var_dump(property_exists($a, "b")); // true var_dump(isset($a->b)); // false (as $a->b is undefined) var_dump($a->b); // null and emits a notice ($a->b is undefined) It's true that you can trick code using it (wrongly); that code probably should be using isset(). property_exists() is really only meant to check the existence of declaration or it actually having a value. Previous Comments: ------------------------------------------------------------------------ [2016-05-12 13:19:29] pierre dot rineau at makina-corpus dot com Yes, it is either one of: - property_exists() should not return true for unset() properties - unset() un-declares statically declared class properties ------------------------------------------------------------------------ [2016-05-11 13:58:06] nikic@php.net To clarify, the "bug" you are reporting here is that property_exists() returns true for properties that have been unset? ------------------------------------------------------------------------ [2016-05-11 11:16:03] pierre dot rineau at makina-corpus dot com https://3v4l.org/3sAs5 ------------------------------------------------------------------------ [2016-05-11 11:12:50] pierre dot rineau at makina-corpus dot com Changed title. ------------------------------------------------------------------------ [2016-05-11 11:11:47] pierre dot rineau at makina-corpus dot com Description: ------------ If you declare a class with declared properties, you might want to use unset() to reset the property value to null, but when accessing it later, it causes a "undefined property" warning. This seems legit, but it becomes tricky once you notice that property_exists() returns true before calling unset(), which is the wanted behavior since the property is declared (even when uninitialized), but it also returns true after calling unset(), which is incompatible with the "undefined property" warning. It seems to always have worked this way, but any code using property_exists() will be tricked by the false positive. [someuser@localhost] ~/current > php -v PHP 5.5.25 (cli) (built: May 14 2015 10:02:12) Copyright (c) 1997-2015 The PHP Group Zend Engine v2.5.0, Copyright (c) 1998-2015 Zend Technologies with Zend OPcache v7.0.4-dev, Copyright (c) 1999-2015, by Zend Technologies with Xdebug v2.4.0RC2, Copyright (c) 2002-2015, by Derick Rethans [someuser@localhost] ~/current > php -a Interactive shell php > class A { public $b; }; php > $a = new A; php > echo property_exists($a, 'b'); 1 php > $a->b; php > unset($a->b); php > echo property_exists($a, 'b'); 1 php > $a->b; PHP Notice: Undefined property: A::$b in php shell code on line 1 PHP Stack trace: PHP 1. {main}() php shell code:0 php > pounard@guinevere] ~ > php -v PHP 7.0.6 (cli) (built: May 1 2016 07:39:38) ( NTS ) Copyright (c) 1997-2016 The PHP Group Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies with Xdebug v2.4.0, Copyright (c) 2002-2016, by Derick Rethans [pounard@guinevere] ~ > php -a PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php/modules/redis.so' - /usr/lib/php/modules/redis.so: undefined symbol: zval_used_for_init in Unknown on line 0 Interactive shell php > class A { public $b; }; php > $a = new A; php > echo property_exists($a, 'b'); 1 php > $a->b; php > unset($a->b); php > echo property_exists($a, 'b'); 1 php > $a->b; PHP Notice: Undefined property: A::$b in php shell code on line 1 PHP Stack trace: PHP 1. {main}() php shell code:0 php > Test script: --------------- class A { public $b; }; $a = new A; echo property_exists($a, 'b'); // Returns '1' $a->b; // Remains silent unset($a->b); echo property_exists($a, 'b'); // Still returns '1' $a->b; // Cause a "Notice: Undefined property A::$b" ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=72194&edit=1