protected function storeCallback(\Closure $callback)
    {
        $key = md5(microtime());
        $this->callbacks[$key] = $callback;
        return $key;
    }
protected function storeCallback(\Closure $callback)
    {
        $key = md5(microtime());
        $this->callbacks[$key] = $callback;
        return $key;
    }
protected function storeCallback ( \ Closure $ callback ) { $ key = md5 ( microtime ( ) ) ; $ this -> callbacks [ $ key ] = $ callback ; return $ key ; }
Store a callback index by a generated key

@param callable $callback
@return string $key
Store a callback index by a generated key