It is standard in STL to have two ranges that are zipped together (such as in the two-input-sequence version of std::transform at http://www.sgi.com/tech/stl/transform.html) where the first range has begin and end iterators and other ranges have only begin iterators. However, boost::zip_iterator does not support this capability because it compares all iterators in the iterator tuple. Therefore, it is not possible to write std::transform on two sequences by using a zip_iterator to join the sequences. Allowing this by only comparing the first elements in the iterator tuples would simplify the code for zip_iterator, although it would no longer allow the zipping of zero sequences unless that was special-cased. Is this a reasonable feature to allow? I could probably put together a patch for it in the next few days if people wanted it. -- Jeremiah Willcock