Frankly, I am disconcerted that the original code runs through a float conversion in the first place. This is not as much about removing a warning rather than fixing bad code since the warning had a point.
https://codereview.appspot.com/581400043/diff/577250043/flower/rational.cc File flower/rational.cc (right): https://codereview.appspot.com/581400043/diff/577250043/flower/rational.cc#newcode50 flower/rational.cc:50: else if (sign_ == -1 || sign_ == 1 That's unreadable and "assert (false)" is not a useful assertion to print out. Instead this should not even contain an else if branch (which is entirely pointless if the if branch ends in return). The whole function body could just be assert (sign_ >= -2 && sign <= 2); return sign_ != 0; but I don't think the assertion is even warranted. Why check for stuff that the function doesn't need to work? https://codereview.appspot.com/581400043/
