src/Common/Util/MapUtil.php
public static function arrayToKey(array $array): string {
        $result = "";
        \array_walk_recursive($array, function ($key, $value) use (&$result) {
            $result .= $key . $value;
        });
        return $result;
    }
public static function arrayToKey(array $array): string {
        $result = "";
        \array_walk_recursive($array, function ($key, $value) use (&$result) {
            $result .= $key . $value;
        });
        return $result;
    }
public static function arrayToKey ( array $ array ) : string { $ result = "" ; \ array_walk_recursive ( $ array , function ( $ key , $ value ) use ( & $ result ) { $ result .= $ key . $ value ; } ) ; return $ result ; }
converts an array to a valid key for HashMap

@param array $array
@return string
converts an array to a valid key for HashMap