public function trace(string $operation): int
    {
        $this->buffTrace[] = [
            'operation' => $operation, 
            'time'      => microtime(true), 
            'result'    => '', 
            'stack'     => 9 == self::C_DEBUG_LEVEL ? debug_backtrace(): null, 
        ];
        return count($this->buffTrace) - 1;
    }