Isn't this const auto& redundant?

Question

I found this code in one of Stroustrup's books:

void print_book(const vector<Entry>& book) {      for (const auto& x : book) // for "auto" see §1.5            cout << x << '\n'; } 

But the const seems redundant because x will be deduced to be a const_iterator since book is const in the parameter. Is const auto really better?

Answer 1

In my opinion, it looks explicit which is why it is better. So if I mean const, then I'd prefer to write it explicitly. It enhances local reasoning and thus helps others to understand the code comparatively easily — other programmers dont have to look at the declaration of book and infer that x is const as well.