_wp_filter_build_unique_id example

    public function add_filter( $hook_name, $callback, $priority, $accepted_args ) {
        $idx = _wp_filter_build_unique_id( $hook_name, $callback, $priority );

        $priority_existed = isset( $this->callbacks[ $priority ] );

        $this->callbacks[ $priority ][ $idx ] = array(
            'function'      => $callback,
            'accepted_args' => $accepted_args,
        );

        // If we're adding a new priority to the list, put them back in sorted order.         if ( ! $priority_existed && count( $this->callbacks ) > 1 ) {
            ksort( $this->callbacks, SORT_NUMERIC );
        }