Should I use std::move when moving local variables?

Question

Consider the below code:

Bar my_f()
{
    Foo f{args,to,create,foo};
    Bar b{std::move(f),other,args}; //Is move here unnecessary?

    // code that does not use f;

    return b;
}

Is compiler required to check {code that does not use f} and automatically move f into b?

It is very unlikely the compiler will move `f`. It may do something more efficient and easy to implement, as long as it follows the as-if rule. There's a duplicate somewhere. — juanchopanza, May 07 '14 at 20:40
There is no guarantee that the compiler would do that...I doubt a compiler would do that automatically because it would break scoping rules. — IdeaHat, May 07 '14 at 20:40

score 5 · Answer 1 · answered May 07 '14 at 20:40

The compiler will not automatically move the object into the constructor of Bar, just because f is not used afterwards. If you want to move f, either make it explicit with std::move(f) or remove the named variable:

Bar b{Foo{args, to, create, foo}, other, args}; // will automatically move (if possible)

Should I use std::move when moving local variables?

1 Answers1