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Bug #34795 Passing assignment result by reference passes it by value
Submitted: 2005-10-09 20:58 UTC Modified: 2005-10-20 16:45 UTC
From: tomas_matousek at hotmail dot com Assigned: dmitry (profile)
Status: Not a bug Package: Scripting Engine problem
PHP Version: 5CVS-2005-10-09 OS: *
Private report: No CVE-ID: None
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 [2005-10-09 20:58 UTC] tomas_matousek at hotmail dot com 
Description:
------------
Let's have a function with a parameter passsed by reference.

function f(&$x) { }

Now, call this function as follows:

f($a = $b = $c);

This will sometimes fail sometimes not depending on whether any of the variables $a, $b, $c has previously been used with =& operator. In a such case, the call succeeds with $a being aliased to $x. Otherwise, fatal error occures: "Only variables can be passed by reference".

this code works:

$b =& $z;
f($a = $b = $c);

this code doesn't:

f($a = $b = $c);

So the "correctness" of the code depends on whether there exists an alias of one of the variable. That's weird, isn't it?



Reproduce code:
---------------
$b =& $z;
f($a = $b = $c);

f($u = $v = $w);


Expected result:
----------------
OK. 
OK.

- or -

Error.
Error.


Actual result:
--------------
OK.
Error.

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 [2005-10-09 21:11 UTC] sniper@php.net 
Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip
 [2005-10-09 21:58 UTC] tomas_matousek at hotmail dot com 
Well, the versino in CVS doesn't report an error, however it passes by value instead which is imho also incorrect. 
Example:

function f(&$x)
{
  $x = 10;
}

$a = $b = $c = $d = $u = $v = $w = 1;

$b =& $z;
f($a = $b = $c);

var_dump($a,$b,$c);

f($u = $v = $w);

var_dump($u,$v,$w);

--------

prints:
int(10)
int(1)
int(1)
int(1)
int(1)
int(1)

It should print
int(10)
int(1)
int(1)
int(10)
int(1)
int(1)
 [2005-10-09 22:41 UTC] sniper@php.net 
Dmitry, can you check this out?
 [2005-10-12 12:58 UTC] tony2001@php.net 
"$u = $v = $w" is an expression, not a variable. 
It's not possible to reference an expression and I don't think it can be fixed at all.
 [2005-10-12 14:05 UTC] tomas_matousek at hotmail dot com 
"$x =& $y" is also an expression, isn't it?
And f($x =& $y) works well.
 [2005-10-20 16:45 UTC] iliaa@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

This is expected and documented behaviour.
 
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