c++ - Is it safe to store a changing object in a stl set? -

i want container store unique std::weak_ptrs. std:set requires operator<, presumably because stores items in tree. worry if implement operator< in obvious way (destroyed ptr = null ptr < valid ptr) result can mutate after items added container, may break it.

is in fact safe? if not, suggestions container?

thanks

you cannot use weak_ptrs keys unless use owner based comparison (against value based one, not defined weak_ptr, trying use operator< results in error). problem can expire , ordering of containers (a set map) wouldn't consistent anymore.

as correctly pointed out kerrek sb (forgive me, mobile app not let me correctly link users) , can read link in comments, can rely on std::owner_less starting c++11.

a valid approach use set defined follows:

std::set<std::weak_ptr<c>, std::owner_less<std::weak_ptr<c>>> 

note owner_less can less verbose, deduces type automatically.

keep in mind approach not keep invoking expired method while visiting set, because can still contains expired objects if consistently ordered.

also, note there huge difference between expired weak_ptr , empty one, owner based comparison not intuitively, if expiration shouldn't affect once used approach above mentioned.

here some links.