I know this has come up before, so I'm really seeking to discover the current situation.

boost::size( std::list<...> ) fails because the implementation of size is end - begin.

I know I could use distance, but am surprised size(list) doesn't work out of the box.

* So, is it correct that size(list) doesn't work?

* Does distance(begin, end) specialise for random access iterators to O(n) performance?

* Why doesn't size similarly specialise?

size() and distance() have different purposes. size() is for when you want to know the size of a range in constant time, and do something else if it cannot be determined in constant time. distance() is for when you want to know the size of a range regardless of whether it takes constant time or linear time to calculate. Note that Boost.Range provides a distance(range) overload of distance, so it's not any more verbose to use than size() if your use case is the second one. Regarding std::list, there are different stories for C++98 and C++11: In C++98, the complexity of std::list::size() was not guaranteed to be constant [1]. My understanding is that some implementations didn't keep track of the size in order to implement constant-time splice(), and consequently their size() was linear-time. So I think that it is not reasonable to expect that size() works for std::list in C++98. In C++11, however, the complexity of std::list::size() is guaranteed to be constant [1]. Therefore, I think it would be reasonable if in C++11, Boost.Range provided a specialized version of size() for std::list that forwarded to std::list::size(). This has not been implemented yet. If you would like to see it implemented, please file a Trac ticket. If no one objects to this addition, I will implement it when I get a chance. Regards, Nate [1] http://www.cplusplus.com/reference/list/list/size/