auto&& is called a forwarding reference (also referred to as a universal reference). It can bind to anything which makes it useful for certain cases. Forwarding references will, just like const references, extend the lifetime of a temporary. But in contrast to the const reference, auto&& allows you to mutate objects it references, temporaries included.
Use auto&& for variables that you only forward to some other code. In those forwarding cases you rarely care about whether the variable is a const or a mutable, you just want to pass it to some code that actually going to use the variable.
It's important to note that only auto&& and T&& in a template method are forwarding references. Using the && syntax with an explicit ...
