According to http://www.cplusplus.com/reference/list/list/size/, list::size must be constant time in C++11.

That may make 'splice' slower. See http://home.roadrunner.com/~hinnant/On_list_size.html (I think that could be solved by having list iterators carry a field pointing to their container, but haven't given it much thought. Corrections welcome)

Having list iterators carry a field pointing to their container wouldn't help you determine the number of objects between two iterators when you splice, which is what you need in order to maintain the object count.

Storing an index in the iterator would not be a solution either. That would mean updating the index in all the existing iterators when you insert an object in the list.

Of course. Thanks.

It changes the ABI of std::list, which is a serious concern.

... and figuring out how to deal with that is the reason that libstdc++ is moving slowly on this.

libc++ has the luxury of assuming c++11.

No, really, it's quite a safe assumption.

Hell, you probably lose that much to padding somewhere anyways.

Then you might be better off with a std::forward_list which is typically the size of a pointer.