Should I move a temporary into a variable?

Question

If I have an existing non-trivial variable and I want to re-assign it with new contents that I will declare on the same line as the assignment, should I use move semantics?

My question comes from the following scenario:

std::vector<string> existing = { ... };

int main(int argc, char *argv[]){
    const char *bunch_of_strings = ... ;
    std::stringstream ss(bunch_of_string);

    existing = std::move(std::vector<std::string>(std::istream_iterator<std::string>(ss), {}));
}

should I be doing this, will the compiler optimize it similarly if I don't, or is it just better not to?

Answer 1

std::move is redundant there. The purpose of move is to treat a variable as a temporary (more accurately, an rvalue) when it's not (or might not be). If it's already an rvalue, it will certainly be moved if possible anyway.