PHP :: Request #60944 :: Unable to detect if variable exists vs. is null

[2012-02-01 08:05 UTC] lampacz+php at gmail dot com

Description:
------------
There is no difference between $x = NULL and unset($a). So i'm unable to detect if variable was defined (so it can be defined and be filled with null)

http://www.php.net/manual/en/types.comparisons.php Table Comparisons of $x with PHP functions, rows 2 - 4 gives same results


Expected result:
----------------
Different results for undefined variables and null variables

[2012-02-01 09:54 UTC] laruence@php.net

<?php
$a = null;
var_dump(array_key_exists('a', get_defined_vars())); //or $GLOBALS
?>

[2012-02-01 10:39 UTC] lampacz+php at gmail dot com

Marvelous.

Sugestion for new function: is_defined(mixed $var)

which internally return array_key_exists($var, get_defined_vars()); ?

Thank you for.

[2012-02-02 02:00 UTC] phpmpan at mpan dot pl

What is the rationale for introducing such function? Can you provide any real-life example when it is neccessary to distinguish between an undefined global variable and a global variable set to `NULL`? The question is important, as use of global variables is getting less popular. Adding a new function, that will duplicate already existing functionality (proposed by Laruence), is IMHO not a good idea.

[2012-02-03 09:00 UTC] laruence@php.net

-Status: Open +Status: Wont fix

[2012-02-03 09:00 UTC] laruence@php.net

php is a loose-type language. there is no different between a null and a 
`undefined variable` . 

as I said above, you can use isset($GLOBALS[***]) to achieve your requirement.

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