Forcing auto to be a reference type in a range for loop

Question

Suppose I have foo which is a populated std::vector.

I need to operate on the elements of this vector. I\'m motivated to writ

Answer 1

I would use auto&&:

for (auto&& it : foo) {
    // bla
}

The reason is spelt out in N3994 "Range-Based For-Loops: The Next Generation (Revision 1)" that it would better work with proxy objects (such as those coming from std::vector).

In fact, that proposal for C++1z (supported already by Clang 3.5 SVN in -std=c++1z mode) proposes the syntax:

// c++1z only
for (it : foo) { 
    // bla
}

as a short-hand for for (auto&& it : foo).

Update: the N3994 proposal was not voted into the C++17 working paper.