template <typename R>
class shared_future
{
...
// move support
shared_future(shared_future && other);
shared_future(unique_future<R> && other);
shared_future& operator=(shared_future && other);
shared_future& operator=(unique_future<R> && other);
...
}
这些双括号究竟是什么?我浏览了“BS C ++ Langauge 3d版”并找不到任何解释。