Usort() expects parameter 2 to be a valid callback error in php7 - but works fine in php 5.6

Question

So i have this sorting of multi-dimensional array:

function score($somearray) {
            $scores = 0;
        if (($somearray[4] == '') AND (($somearray[5] == '') OR ($somearray[5] == '00:00:00')) AND (($somearray[6] == '') OR ($somearray[6] == '00:00:00'))) { // days are not set and time is not set
        $scores = 1;
        }
            
        else if (($somearray[4] != '') AND (($somearray[5] == '') OR ($somearray[5] == '00:00:00')) AND (($somearray[6] == '') OR ($somearray[6] == '00:00:00'))) { // days are set and time is not set
        $scores = 2;
        }
        
        else if (($somearray[4] == '') AND ((($somearray[5] != '') AND ($somearray[5] != '00:00:00')) OR (($somearray[6] != '') AND ($somearray[6] != '00:00:00')))) { // days are not set and time is set
        $scores = 3;
        }
        
        else if (($somearray[4] != '') AND ((($somearray[5] != '') AND ($somearray[5] != '00:00:00')) OR (($somearray[6] != '') AND ($somearray[6] != '00:00:00')))) { // days are set and time is set
        $scores = 4;
        }
        return $scores;
        }

function cmp2(array $a, array $b) 
    { 
        
        return (score($b) - score($a)); 
        
    }

$recordsarr = array();

$recordsarr[0] = ['1','5','2022-04-05','2022-04-15', '', '10:30:00', '11:30:00', '1', '800'];
$recordsarr[1] = ['1','5','2022-04-01','2022-04-20', '5', '10:30:00', '11:30:00', '1', '700'];
$recordsarr[2] = ['1','5','2022-04-05','2022-04-15', '4', '', '', '1', '800'];
$recordsarr[3] = ['1','0','2022-04-07','2022-04-15', '', '', '', '1', '800'];
$recordsarr[4] = ['1','5','2022-04-06','2022-04-16', '', '', '', '0', '900'];
$recordsarr[5] = ['1','5','2022-04-07','2022-04-12', '2', '', '', '0', '600'];
    
$majorpriorityarray = array();

 if (count($recordsarr) > 0) {
 usort($recordsarr, 'cmp2');
 $majorpriorityarray = $recordsarr[0];
                }
echo "major priority array is<br>";
var_dump($majorpriorityarray);

It works fine in php5.6, but does not work in php7, showing this error:

usort() expects parameter 2 to be a valid callback, function 'cmp2' not found or invalid function name

What i have to change in my code for working this sorting stuff in php7? Thanks

UPD: Just tried:

usort($recordsarr, function($a, $b) {
    cmp2($a, $b);
});

Also tried:

function cmp2(array $a, array $b) 
    { 
return score($b) <=> score($a);     
    }

Both these variants does not show an error, but are not sorting - do not affect the initial order.

Answer 1

Try to use

usort($recordsarr, array( $this, "cmp2" ));