When should I use forward and move?

Question

I have a code that operates on a vector:

template
void doVector(vector& v, T&& value) {
    //....
    v.push_back(value);         


        

Answer 1

• When passing a parameter that's a forwarding reference, always use std::forward.
• When passing a parameter that's an r-value, use std::move.

E.g.

template 
void funcA(T&& t) {
    funcC(std::forward(t)); // T is deduced and therefore T&& means forward-ref.
}

void funcB(Foo&& f) {
    funcC(std::move(f)); // f is r-value, use move.
}

Here's an excellent video by Scott Meyers explaining forwarding references (which he calls universal references) and when to use perfect forwarding and/or std::move:

C++ and Beyond 2012: Scott Meyers - Universal References in C++11

Also see this related question for more info about using std::forward: Advantages of using forward