variable_exists() patch View as Markdown

I am not really convinced either that variable_exists() is
function_exists() parallel.
Under what circumstances is this needed?

Andi

The followup I sent to Ilia gives examples of how this patch can be
used to determine whether, for instance, array keys exist, without
having to use the array_key_exists() workaround; also, you can check
whether an object has defined an attribute, even if it hasn't yet
assigned it a value:

<?php
class foo {
var $bar;
var $baz = null;
var $quux = 'quux';
}
$foo = new foo;

echo "variable_exists($foo->bar): " . (variable_exists($foo->bar) ?
'yes' : 'no') . " (should be yes)\n";
echo "variable_exists($foo->baz): " . (variable_exists($foo->baz) ?
'yes' : 'no') . " (should be yes)\n";
echo "variable_exists($foo->quux): " . (variable_exists($foo->quux)
? 'yes' : 'no') . " (should be yes)\n";
echo "variable_exists($foo->quuux): " .
(variable_exists($foo->quuux) ? 'yes' : 'no') . " (should be no)\n";

echo "isset($foo->bar): " . (isset($foo->bar) ? 'yes' : 'no') . "
(should be yes)\n";
echo "isset($foo->baz): " . (isset($foo->baz) ? 'yes' : 'no') . "
(should be yes)\n";
echo "isset($foo->quux): " . (isset($foo->quux) ? 'yes' : 'no') . "
(should be yes)\n";
echo "isset($foo->quuux): " . (isset($foo->quuux) ? 'yes' : 'no') .
" (should be no)\n";
?>

...the output from the above is:

variable_exists($foo->bar): yes (should be yes)
variable_exists($foo->baz): yes (should be yes)
variable_exists($foo->quux): yes (should be yes)
variable_exists($foo->quuux): no (should be no)
isset($foo->bar): no (should be yes)
isset($foo->baz): no (should be yes)
isset($foo->quux): yes (should be yes)
isset($foo->quuux): no (should be no)

etc. It's a little annoying at times that that isset() doesn't do what
its name suggests it should, which leads people to try to use it
for things which is seems that it should be able to do, but can't. When
I've tried to explain it, the only answer I can give is "Sorry, that's
just the way it is--and no, you can't do that in PHP".

It seems basic enough functionality that is almost, but not quite,
satisfied by isset().

--
Torben Wilson torben@php.net +1.604.709.0506
http://www.thebuttlesschaps.com http://www.inflatableeye.com
http://www.hybrid17.com http://www.themainonmain.com
-----==== Boycott Starbucks! http://www.haidabuckscafe.com ====

Ilia Alshanetsky wrote:

Do we really need this function? I see 2 ways of 'implementing' this
functionality in PHP without having to add another function. For example:
(isset($var) || is_null($var)) or gettype($var).

Ilia

I for one would like to see something like variable_exists(), as I am
very annoyed with
the logic of isset() returning false if the variable exists and has a
value of null.

The name of the function in this case doesn't not fit the logic for
isset(). The variable does exist and it IS in fact set, the value just
so happens to be null.
I constantly get puzzled looks and confusion, when I explain to folks
that are new to php, that isset() really doesn't do what it's name
suggests.

I for one would much rather do
if ( variable_exists($var) ) {} versus
if (isset($var) || is_null($var)) {}

it's less code to type and is less prone to errors.

So I would like to see the patch in, or something similar in
functionality, since isset() doesn't do what I'd expect.
Walt

Do we really need this function? I see 2 ways of 'implementing' this
functionality in PHP without having to add another function. For example:
(isset($var) || is_null($var)) or gettype($var).

Ilia

Those ideas don't do the same thing, though. Try it with arrays:

-SNIP------------------------------------------------------------

Array testing with variable_exists()
$arr = array(1 => null, 2 => array(1 => 3, 2 => null));

variable_exists($arr[1]): yes (should be yes)
variable_exists($arr[2]): yes (should be yes)
variable_exists($arr[3]): no (should be no)
variable_exists($arr[1][2]): no (should be no)
variable_exists($arr[2][1]): yes (should be yes)
variable_exists($arr[2][2]): yes (should be yes)
variable_exists($arr[2][3]): no (should be no)

Array testing with gettype()
$arr = array(1 => null, 2 => array(1 => 3, 2 => null));

gettype($arr[1]): yes (should be yes)
gettype($arr[2]): yes (should be yes)

Notice: Undefined offset: 3 in /home/torben/public_html/phptest/variable_exists.html on line 40

gettype($arr[3]): yes (should be no)
gettype($arr[1][2]): yes (should be no)
gettype($arr[2][1]): yes (should be yes)
gettype($arr[2][2]): yes (should be yes)

Notice: Undefined offset: 3 in /home/torben/public_html/phptest/variable_exists.html on line 44

gettype($arr[2][3]): yes (should be no)

Array testing with (isset() || is_null())
$arr = array(1 => null, 2 => array(1 => 3, 2 => null));

(isset($arr[1]) || is_null($arr[1])): yes (should be yes)
(isset($arr[2]) || is_null($arr[2])): yes (should be yes)

Notice: Undefined offset: 3 in /home/torben/public_html/phptest/variable_exists.html on line 51

(isset($arr[3]) || is_null($arr[3])): yes (should be no)
(isset($arr[1][2]) || is_null($arr[1][2])): yes (should be no)
(isset($arr[2][1]) || is_null($arr[2][1])): yes (should be yes)
(isset($arr[2][2]) || is_null($arr[2][2])): yes (should be yes)

Notice: Undefined offset: 3 in /home/torben/public_html/phptest/variable_exists.html on line 55

(isset($arr[2][3]) || is_null($arr[2][3])): yes (should be no)
-SNIP------------------------------------------------------------

--
Torben Wilson torben@php.net +1.604.709.0506
http://www.thebuttlesschaps.com http://www.inflatableeye.com
http://www.hybrid17.com http://www.themainonmain.com
-----==== Boycott Starbucks! http://www.haidabuckscafe.com ====

exactly why isset() is either

1. a bad name for the function or
2. 'broken'

Wrong. isset() has a very proper name "is-set", which to me and other people
says that it will see if a variable is set (has a value). It does this job
admirably and it certainly not broken. Documentation specifies how this
function will perform perfectly.

Ilia