private function addHelper(string $name, string $path): void
    {
        $class = static::class;

        // create store of helpers for this class
        if (!isset(static::$helpers[$class])) {
            static::$helpers[$class] = [];
        }

        $helper = include $path;

        if (\is_callable($helper)) {
            static::$helpers[$class][$name] = $helper;
        } else {
            throw new CommonException("Helper `$name` not found in file `$path`");
        }
    }