Oops, you're right of course; I got reference collapsing rules confused with the regular binding rules. Proxy objects will only bind to auto const& or auto&&, t

Oops, you're right of course; I got reference collapsing rules confused with the regular binding rules. Proxy objects will only bind to auto const& or auto&&, though, since they're generally returned by value. I was surprised to see that this does not come up in std::bitset nor std::valarray, but only std::vector<bool>.