This doesn't help to solve the original problem of avoiding the copy. Your calls to big_object_ptr.reset(...) will cause the BigObject copy constructor t

This doesn't help to solve the original problem of avoiding the copy. Your calls to big_object_ptr.reset(...) will cause the BigObject copy constructor to be called. The object pointed to by unique_ptr does not have the same storage as the objects "foo" and "bar". At the very least, you need to do big_object_ptr.reset(std::move(foo)); which will cause foo to be moved into the unique_ptr's storage. In code like this, you should just use make_unique, in which case the BigObject is constructed in place, and unique_ptr can be RVO'ed: if (...) { return make_unique<BigObject>(...); } else ...