Why isn't operator[] overloaded for lvalues and rvalues?

Question

The standard C++ containers offer only one version of operator[] for containers like vector and deque. It returns a

Answer 1

I think you will leave the container in an invalid state if you move out one of the elements, I would argue the need to allow that state at all. Second, if you ever need that, can't you just call the new object's move constructor like this:

T copyObj = std::move(makeVector()[0]);

Update:

Most important point is, again in my opinion, that containers are containers by their nature, so they should not anyhow modify the elements inside them. They just provide a storage, iteration mechanism, etc.