php: write isset function which returns value or null

Question

I have the following code in numerous places (thousands of places) around my project:

$foo = isset($mixed) ? $mixed : null;

Where $mixed can be anything: array, array element, object, object property, scalar, etc. For example:

$foo = isset($array['element']) ? $array['element'] : null;
$foo = isset($nestedArray['element']['key']) ? $nestedArray['element']['key'] : null;
$foo = isset($object->prop) ? $object->prop : null;
$foo = isset($object->chain->of->props) ? $object->chain->of->props : null;

Is there a way to write this repeated logic as a (simple) function? For example, I tried:

function myIsset($mixed)
{
    return isset($mixed) ? $mixed : null;
}

The above function looks like it would work, but it does not in practice. For example, if $object->prop does not exist, and I call myIsset($object->prop)), then I get fatal error: Undefined property: Object::$prop before the function has even been called.

Any ideas on how I would write such a function? Is it even possible?

I realize some solutions were posted here and here, but those solutions are for arrays only.

I don't think you can do that more efficiently. Instead I would try to reduce the number of times you use it, *thousands* seems far too much. I would guess that whole blocks of variables are either set or not so checking for one could give you the opportunity to set various. — jeroen, Jan 12 '15 at 22:55
@jeroen It is a "code smell" if you're having to check this so often everywhere — Ruan Mendes, Jan 12 '15 at 22:57

score 11 · Answer 1 · answered May 23 '18 at 13:03

11

PHP 7 has a new "Null coalescing operator" which does exactly this. It is a double ?? such as:

$foo = $mixed ?? null;

See http://php.net/manual/en/migration70.new-features.php

answered May 23 '18 at 13:03

Paul

669
8
9

Thank you for pointing this out! This is easy and simple build-in little function. – radzi0_0 Nov 18 '21 at 19:18

score 9 · Accepted Answer · answered Jan 30 '15 at 21:56

I stumbled across the answer to my own question while reading about php references. My solution is as follows:

function issetValueNull(&$mixed)
{
    return (isset($mixed)) ? $mixed : null;
}

Calls to this function now look like:

$foo = issetValueNull($array['element']);
$foo = issetValueNull($nestedArray['element']['key']);
$foo = issetValueNull($object->prop);
$foo = issetValueNull($object->chain->of->props);

Hopefully this helps anyone out there looking for a similar solution.

Ruan Mendes · Answer 3 · 2015-01-13T14:08:42.730

isset is a language construct, not a regular function. Therefore, it can take what would otherwise cause an error, and just return false.

When you call myIsset($object->prop)), the evaluation occurs and you get the error.

See http://php.net/manual/en/function.isset.php

This is the same problem as using typeof nonExistentVariable in JavaScript. typeof is a language construct and will not cause an error.

However, if you try to create a function, you get an error for trying to use an undefined variable.

function isDef(val) {
    return typeof val !== 'undefined';
}

console.log( typeof nonExistent !== 'undefined'); // This is OK, returns false
isDef(nonExistent); // Error nonExistent is not defined

score -1 · Answer 4 · answered Jan 12 '15 at 22:51

-1

You could actually just write it like:

$foo = $mixed?:null;

answered Jan 12 '15 at 22:51

rm-vanda

3,122
3
23
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No, that would generate a warning if `$mixed` is not set. – jeroen Jan 12 '15 at 22:52
It would generate a Notice. And you have no business having notices or warnings being displayed in a production environment. – rm-vanda Jan 13 '15 at 13:05
If you're writing code like that, you might as well skip that whole ternary expression as an unset variable evaluates to `NULL`. – jeroen Jan 13 '15 at 13:15
No, just `$foo = $mixed;`. That would result in `$foo === NULL` if `$mixed` is not set. – jeroen Jan 13 '15 at 16:03
1

Haha, good point ! - that sorta makes this whole question useless. – rm-vanda Jan 13 '15 at 16:20

score -2 · Answer 5 · answered Jan 12 '15 at 22:52

-2

If you just want to check if it exist do this

function myIsset($mixed)
{
    return isset($mixed); // this is a boolean so it will return true or false
}

answered Jan 12 '15 at 22:52

Rafael

7,605
13
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2

Why write a function which just returns the result of a global function? Semantics? – Leo Jan 30 '15 at 18:41
2

i agree it is redundant. – Rafael Oct 19 '15 at 13:44

score -2 · Answer 6 · edited Oct 19 '15 at 11:34

-2

function f(&$v)
{
    $r = null;

    if (isset($v)) {
        $r = $v;
    }

    return $r;
}

edited Oct 19 '15 at 11:34

smottt

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answered Oct 16 '15 at 18:51

ismavolk

115
2
3

php: write isset function which returns value or null

6 Answers6