Callback function using variables calculated outside of it
Solution 1:
You can use the use
keyword to inherit variables from the parent scope. In your example, you could do the following:
$callback = function($val) use ($avg) { return $val < $avg; };
For more information, see the manual page on anonymous functions.
If you're running PHP 7.4 or later, arrow functions can be used. Arrow functions are an alternative, more concise way of defining anonymous functions, which automatically capture outside variables, eliminating the need for use
:
$callback = fn($val) => $val < $avg;
Given how concise arrow functions are, you can reasonably write them directly within the array_filter
call:
return array_filter($arr, fn($val) => $val < $avg);