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);
...
}
那些双&号到底是什么?我浏览了“BS The C++ Langauge 3d edition”,但找不到任何解释。