[ben-schaaf]

No, it is not statically knowable if it is actually moved.

    void foo(Obj && arg) {}

Does not move `arg`. It's fairly easy to write code that assumes `std::move` moves the value, but that can lead to bugs. For example:

    void some_function(std::vector<int> &&);
    void some_function2(std::vector<int> &&);

    void main() {
        std::vector<int> a = { 1 };
        some_function(std::move(a));

        a.push_back(2);
        some_other_function(std::move(a));
    }

The expectation is that `some_other_function` is always called with `{ 2 }`, but this will only happen if `some_function` actually moves `a`.

[tsimionescu]

You're right, of course - I was completely messing up in my mind what r-value reference parameters actually do, and thinking that they need to be moved to, when the whole point is that they don't, they're just a reference.

[adrianN]

Is pushing to a moved-from vector even legal? I thought in general the only guarantee you have after a move is that is save to destruct the object.

[ben-schaaf]

The state of a moved-from value is valid but unspecified (note, not undefined). IIRC the spec says vector must be `empty()` after a move. So all implementations do the obvious thing and revert back to an empty vector.