From: "Peter C. Verhage" <peter@...>
Date: 2007-10-03T07:18:22+09:00
Subject: Re: Reference vs. Reference

Hi,

In PHP 4 and 5 you have references which work similar like C++ 
references.  E.g. you can make a variable reference another variable 
after which if you change the value of one of those variables the other 
variable's value will also be "updated". An example:

$x = 1;
$y = &$x; // y references x
$x = 2;
echo $y; // 2
$y = 3;
echo $x; // 3

In PHP 4 you always had to pass objects by reference if you didn't want 
to end up with a copy of your object.

$x = new Object();
$x->value = 1;
$y = $x; // copy
echo $y->value; // 1
$y->value = 2;
echo $x->value; // 1
$x->value = 3;
echo $y->value; // 2
$y = &$x; // reference
echo $y->value; // 3
$y->value = 4;
echo $x->value; // 4;
$x->value = 5;
echo $y->value; // 5

However, in PHP 5 they introduced a concept similar to the "references" 
we know in Ruby. But because they already used the term "reference" they 
had to come up with a different name, so they call them object handles. 
If you assign an object to a variable you are assigning an object handle 
to the variable. If you assign the value of the first variable to 
another variable you are assigning it the same object handle. So both 
variables "reference" the same object. But if you now assign another 
object to the first (or second) variable, only that variable's content 
changes. E.g.

$x = new stdClass();
$y = $x; // assign object handle
$x->value = 2;
echo $y->value; // 2
$y->value = 3;
echo $x->value; // 3
$x = new stdClass(); // assign different object handle
$x->value = 1;
echo $y->value; // 3

So maybe we should call them handles instead of references to clarify 
the difference?

Regards,

Peter