PHP：＆$这意味着什么？

Question

As I was revieweing PHP sources to find the deprecated call-time-references, I found following 2 things in 3rd party code:

#1
$x = array(&$this, $a, $b);

#2
&$this->foo();

I know that & is meant for marking references. But it makes no sense to me.

In re. #1: When I use array($this) , won't there be a reference saved in the array, too?

In re. #2: When I call foo() of my own instance, why do I need to use $this as reference?

Answer 1

I suppose the code came from PHP4 time.

re #1 - In PHP 4 using array($this) means the same as array(clone($this)) in PHP 5. that is you get a copy of an object instead. In most cases you would like to get the same object though, not its copy. So I suppose the original author used array(&$this) exactly for that reason.

re #2 is explained in Returning References chapter of the manual

in this case it it doesn't matter if it's &$this or some &$obj. The reference in fact is applied to the value returned from foo(). This might make sense for example if foo() has some big static $cache object inside and returns part of it back. E.g.

class MyClass {
  function &foo($id){
    static $cache;
    if (!isset($cache[$id])) {
      $cache[$id] = extract_some_object_from_database($id);
    }
    return $cache[$id];
  }
}

Notice the "&foo"