public function getFailureNames() : array
    {
        if ($this->failures) {
            $keys = array_keys($this->failures);
            $net = [];
            foreach ($keys as $key) {
                if ($key && !ctype_digit('' . $key)) {
                    $net[] = $key;
                }
            }
            return $net;
        }
        return [];
    }
public function getFailureNames() : array
    {
        if ($this->failures) {
            $keys = array_keys($this->failures);
            $net = [];
            foreach ($keys as $key) {
                if ($key && !ctype_digit('' . $key)) {
                    $net[] = $key;
                }
            }
            return $net;
        }
        return [];
    }
public function getFailureNames ( ) : array { if ( $ this -> failures ) { $ keys = array_keys ( $ this -> failures ) ; $ net = [ ] ; foreach ( $ keys as $ key ) { if ( $ key && ! ctype_digit ( '' . $ key ) ) { $ net [ ] = $ key ; } } return $ net ; } return [ ] ; }
Get keys of failures, excluding keys that are numeric.

@return string[]
Get keys of failures excluding keys that are numeric .