$a and $b are completely equal here. $a is not pointing to $b or vice versa. $a and $b are pointing to the same place.
對PHP5中對象和引用的說法是:
A PHP reference is an alias, which allows two different variables to write to the same value. As of PHP 5, an object variable doesn't contain the object itself as value anymore. It only contains an object identifier which allows object accessors to find the actual object. When an object is sent by argument, returned or assigned to another variable, the different variables are not aliases: they hold a copy of the identifier, which points to the same object.
class Person { public $name = 'myName';}$obj = new Person;$assign = $obj;$reference = & $obj;$obj = null;//此操作很重要var_dump($obj);//得到nullvar_dump($assign);//得到object(Person)#1 (1) {["name"]=>string(6) "myName"}var_dump($reference);//得到null