Can you conditionally negate a function in PHP?

For example

$x = true;
return (($x ? "!" : "" ). is_null(NULL));

This obviously doesn't work, is there a way to do it?

The goal is to refactor this

       $var == true
        ? array_filter($labels, function($v){return str_contains($v, 'return');})
        : array_filter($labels, function($v){return !str_contains($v, 'return');});

Thanks

A common way of describing boolean combinations is as a truth table listing the possible inputs and outputs. In this case:

So, the result you want is "either $x is true, or is_null($var) is true, but not both".

Looking in the PHP manual under "logical operators", we see that that's the definition of the xor operator, so you could write this:

return $x xor is_null($var);

An intermediate variable and simple if statement as shown in Justinas's answer is probably a lot more readable, though. Readability is extremely important in programming, because code is read far more times than it's written.

You can, but with different approach: first execute function and then check if it needs to be inverted

$result = is_null($var);

if ($x) {
   // invert result from e.g. true to false
   $result = !$result;
}

is_null returns a boolean. $x is a boolean. Compare both booleans:

return is_null($var) != $x;