Warning:array_filter () expects parameter 2 to be a valid callback

Warning:array_filter () expects parameter 2 to BES a valid callback, function ' checkmonth ' not found or invalid function n Ame in path\to\xxxmodel.php on line 36

Here is the relevant code fragment-PHP version: 5.6:

function Checkmonth ($v) {return $v = = $this->month;}    function Getbymonth ($month) {$ret = $this->allret;    $this->month = isset ($month)? $month:d ate ("M"); Return Array_filter ($ret, "Checkmonth");}

Instead of using the anonymous method is normal, so do not know whether the PHP version of the problem:

function Getcoursebymonth ($month) {$ret = $this->allret;    $month = Isset ($month)? $month:d ate ("M");    Return Array_filter ($ret, function ($item) use ($month) {return date ("M", Strtotime ($item [1])) = = $month; });}

Warning:array_filter () expects parameter 2 to be a valid callback