Are std::streams already movable?

Question

GNU gcc 4.3 partially supports the upcoming c++0x standard: among the implemented features the rvalue reference. By means of the rvalue reference it should be possible to move a non-copyable object or return it from a function.

Are std::streams already movable by means of rvalue reference or does the current library implementation lack something?

Answer 1

In the current g++ svn, rvalue reference support has not yet been added to streams. I suspect adding it will not be too difficult and as ever with open source software, patches are, I'm sure, welcome!

Answer 2

After a quick investigation it comes out that the rvalue reference support has not been added yet to streams.

To return a non-copyable object from a function indeed it is sufficient to implement the move constructor as follows:

struct noncopyable
{
    noncopyable()
    {}

    // move constructor
    noncopyable(noncopyable &&)
    {}

private:
    noncopyable(const noncopyable &);
    noncopyable &operator=(const noncopyable &);
};

Such constructor is supposed to transfer the ownership to the new object leaving the one being passed in a default state.

That said, it is possible to return an object from a function in this way:

noncopyable factory()
{
    noncopyable abc;
    return std::move(abc);
}

While std::stream does not support move constructors it seems that STL containers shipped with gcc 4.3.2 do already support it.