# Feature: Null Coalescing Variable Handling Construct

- Thread: https://externals.io/message/126826
- Original archive: https://news-web.php.net/php.internals/126826
- Started by Robert Chapin on 2025-03-18T15:14:09+00:00
- Messages: 1
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## #126826 — Robert Chapin — 2025-03-18T15:14:09+00:00

URL: https://externals.io/message/126826#126826

Following a brief discussion on Github today about adding operators, I 
decided a simple-looking construct is needed and is arguably a better 
solution for null coalescing comparison.

A common challenge: Need to test the value of a variable whose existence 
is unknown.

Existing solutions:

|$input = $_POST['input'] ?? 'none'; if ($input === 'yes') echo 
'success'; $_POST['input'] ??= 'none'; if ($_POST['input'] === 'yes') 
echo 'success'; |


Needed solution: What we don't have is a Variable Handling Function that 
will concisely resolve any uninitialized variable.

// Hypothetical
|if (nullc($_POST['input']) === 'yes') echo 'success'; |

The proposed construct nullc(mixed $var): mixed, will return the 
original value, or null if the variable is not declared.  This is 
consistent with the construct isset which returns false when a variable 
is assigned to null.  In this way, the two constructs isset and nullc 
will complement each other more concisely than something like the 
construct empty.


The other challenge: Null coalescing operator precedence causes 
unexpected behavior.

$test = 'off';

if ($test ?? '' === 'on') {
     // The line above is equivalent to if ($test ?? false) and will evaluate as true.
     echo 'yes';
}

if ('on' === $what ?? '') {
     // The line above is equivalent to if (('on' === $what) ?? '') and will throw a warning
}

This requires an extra set of parentheses to be workable.

$test = 'off';

if (($test ?? '') === 'on') {
     // The line above will evaluate as false.
}

These nuances were missed in the former Unary Coalesce RFC. Adding or 
not adding an operator doesn't resolve the cumbersome precedence already 
in place for ?? usage.  I was reminded of the need for a function-style 
construct while contemplating the differences between PHP's ?? operator 
and Microsoft's function Nz.  What we can do with an expression like 
nullc($test) === 'on' should be compatible with other existing operators 
and is more elegant than operators-in-parentheses or any multi-line 
statements.  This would also resolve the problem of not being able to do 
the same in a user function.

Further reading:

https://wiki.php.net/rfc/unary_null_coalescing_operator

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Robert Chapin