Usage of std::forward vs std::move

Question

I always read that std::forward is only for use with template parameters. However, I was asking myself why. See the following example:

void Imag         


        

Answer 1

I recommend reading "Effective Modern C ++" by Scott Meyers, specifically:

• Item 23: Understand std::move and std::forward.
• Item 24: Distinguish universal references for rvalue references.

From a purely technical perspective, the answer is yes: std::forward can do it all. std::move isn’t necessary. Of course, neither function is really necessary, because we could write casts everywhere, but I hope we agree that that would be, well, yucky. std::move’s attractions are convenience, reduced likelihood of error, and greater clarity.

rvalue-reference

This function accepts rvalues and cannot accept lvalues.

void ImageView::setImage(Image&& image){
    _image = std::forward(image);        // error 
    _image = std::move(image);           // conventional
    _image = std::forward(image); // unconventional
}

Note first that std::move requires only a function argument, while std::forward requires both a function argument and a template type argument.

Universal references (forwarding references)

This function accepts all and does perfect forwarding.

template  void ImageView::setImage(T&& image){
    _image = std::forward(image);
}