AMDG Mathias Gaunard wrote:
Your code needs to be able to assign a non-empty object to an empty one. Would you also consider it necessary to be able to assign an empty object to a non-empty one?
To be more specific my code needs to assign a non-empty object to one that may or may not be empty.
Possible alternative here: destruct and construct.
replace *write_pos++ = std::move(*begin); by reassign(*write_pos++, std::move(*begin));
with
template<typename T1, typename T2> void reassign(T1& old, T2&& new) { old.~T1(); new(&old) T1(std::forward<T2>(new)); }
A function called `reassign' (that would destroy the old object then construct the new one) could be used instead of assignment in cases where the left operand can be in a `moved' state.
This only provides yet another way to assign (And to get undefined behavior if you forget to use the right function). a = b; // a must not have been moved from a = move(b); // ditto reassign(a, b); // a may have been moved from. doesn't even provide basic exception safety. reassign(a, std::move(b)); // a may have been moved from. Exception safe as long as the move constructor can't throw. I thought that you were advocating safety?
Anyway, I'm pretty sure that function could be purely implemented in terms of swap, which seems like a safer construct.
Sure it could be implemented in terms of swap, but I disagree that swap is safer than proper move assignment. swap is also less efficient for POD. In Christ, Steven Watanabe