Php array_filter not accessing array value by Key

Question

So The below code works as expected and filters out null values and string "undefined" I was getting in my request

$search_params = array_filter(
                    $search_params,
                    function ($val, $key) {
                        return (isset($val) && $val != 'undefined');
                    },
                    ARRAY_FILTER_USE_BOTH
                );

But when I try to do below the function never returns the filtered array e.g always false is returned

$search_params = array_filter(
                    $search_params,
                    function ($val, $key) {
                        return (isset($search_params[$key]) && $val != 'undefined');
                    },
                    ARRAY_FILTER_USE_BOTH
                );

I was wondering what is causing this behavior, is this some kind of context thing?

Answer 1

The global variable $search_params is not in scope inside the function. Use the use() directive to indicate variables that should be inherited into the function's scope.

$search_params = array_filter(
    $search_params,
    function ($val, $key) use ($search_params) {
        return (isset($search_params[$key]) && $val != 'undefined');
    },
    ARRAY_FILTER_USE_BOTH
);