Unexpected result when comparing PHP objects

Question

When I compared two different objects, it returns firstly true, and than after print_r (on objects) returned false.

From PHP manual:

Two object instances are equal if they have the same attributes and values, and are instances of the same class.

But here, in example, I set different values. Why the result is different between PHP 5.4.0 - 5.5.7?

abstract class first {     protected $someArray = array(); }       class second extends first {         protected $someArray = array();             protected $someValue = null;      public function __construct($someValue)     {         $this->someValue = $someValue;     } }      $objFirst = new second('123');            $objSecond = new second('321');             var_dump ($objFirst == $objSecond);         print_r($objFirst);         var_dump ($objFirst == $objSecond); 

Result is:

 bool(true)  second Object ( [someArray:protected] =>  Array ( ) [someValue:protected] => 123 )  bool(false) 

But what I expected was:

  bool(false)   second Object ( [someArray:protected] =>   Array ( ) [someValue:protected] => 123 )   bool(false) 

Answer 1

This was a bug in PHP. It's fixed now, see the commit. In short:

• If you extend a class and redefine the same property the properties_table of the object ends up having a NULL value.
• The comparison code incorrectly aborted comparison when two objects had a NULL value in the properties_table at the same index - reporting the objects as equal. That doesn't make sense of course, because it discards all differences in the following properties. This is fixed now.
• The reason why print_r changes the result, is that by fetching the properties of the object (get_properties) the properties hashtable is rebuilt (rebuild_properties_table) which uses entirely different (and correct) comparison code.
• For context, properties_table and properties are two different ways PHP uses to represent properties - the former being way more efficient and used for declared properties and the latter used for dynamic properties. The print_r call effectively makes the object properties dynamic.