How to use auto with const and & in C++?

Even though the two forms are equivalent in this case, I would choose the first form anyway, since it communicates better the fact that your piece of code does not need to modify the state of the object returned by someMethod().

So my advice is to go for this:

const auto &items = someObject.someMethod();

In your case, there is no difference. The type which auto represents will be deduced to const A in both cases, so the type of items will be const A&.

There is a difference in what the "self-documented semantics" of the code is. The const auto & clearly states "I want a reference to what is returned, and I will not modify it." Just auto & says simply "I want a reference to what is returned."