    public function executable(Executable $executable = null)
    {
        if (func_num_args() > 0) {
            if (!$executable instanceof Closure && !$executable instanceof Executable) {
                throw new App\Exception("Object is not a closure or instance of Coast\App\Executable");
            }
            $this->_executable = $executable;
            return $this;
        }
        return $this->_executable;
    }