C++ STL – Why std::forward_list has no size() method?
N2543 is the proposal, and it has a detailed discussion about size(). The choice between Option 3 [not providing size()] and Option 2 [providing a O(1) size()] is more a matter of judgment. I have chosen Option 3 for the same reason that I chose insert-after instead of insert-before: Option 3 is more consistent with … Read more