When working with C++ standard containers and functions, handling references can sometimes lead to unexpected behavior, particularly with copy semantics. This is where std::ref and std::cref come into play, allowing you to store references in containers and pass them safely to template functions like std::bind or std::thread.

What is std::ref?

by Sandor Dargo

From the article:

Have you heard about std::ref and std::cref? The helper functions that generate objects of type std::reference_wrapper? The answer is probably yes. In that case, this article is probably not for you. But if you haven’t heard about them, or the only usage of std::reference_wrapper you faced was storing references in a vector, then probably it’s worth reading on.

This article is inspired by some failing tests that needed me to use std::ref in order to pass them.

What does reference_wrapper do?

A reference of an object T (T&) is not copy assignable. On the other hand, std::reference_wrapper<T> which emulates T& it both copy-constructible and copy-assignable. It’s even trivially copyable, so copying can take place on a byte level which makes it very efficient.

So when should we use such a wrapper?