s3rvac's comments

I have improved the example in the article to make the code less confusing. Now, a value is assigned to each element in the range and there is no function call.

Using const auto& over const auto makes your code more robust. For example, what if you later decide to change the type of items in the vector from ints to something that is more expensive to copy? You would need to track all uses of the vector and add an ampersand there. And as for the access speed, YMMV but compilers are generally good at optimizations and will drop the reference when it would be faster to just copy the items.