The general rule of thumb for us is "auto is allowed if the type is written on the line somewhere, or if you're writing a for-each of a container, where it has

The general rule of thumb for us is "auto is allowed if the type is written on the line somewhere, or if you're writing a for-each of a container, where it has to be const auto &, unless you have good justification for the copies". The inadvertent copies in for-each constructs are the biggest pitfall for us, because let's just say you don't pick C++ to write software that doesn't have to be as fast as possible :) .