auto vs. auto& vs. auto&& vs. auto const &

Question

I am pretty new to C++ and programming in general. I came across the auto keyword while learning about the different containers and how to use iterators to access each element of the container.

After some research, I figured out that I could simplify the statement in the loop into

auto& it : myMap

compared to its much longer variant.

I did some more research and found that there was also auto&& and auto const &. Can someone give a clear explanation on the difference between all four?

Answer 1

I would say that here is the good explanation: https://stackoverflow.com/questions/29859796/c-auto-vs-auto

Answer 2

I am beginning to understand all but the auto&&. What is the difference between that and auto&?