This email is to determine possible interest in a submission to boost: the combining iterator.
Short Description ================= The combining iterator is another iterator adaptor. It holds a boost::tuple of iterators. Moving the combining iterator in any way causes all member iterators of the tuple to move in parallel. Upon dereferencing the combining iterator, the dereferenced values of the member iterators are supplied as arguments to a client-supplied n-ary functional, and the return value of the functional is returned. The combining iterator is thus a "higher-dimensional transforming iterator." Background and Current Use ========================== The combining iterator grew out of a large software project where a math engine calculates sequences of numbers that are then used by a charting package as data input. The math eninge exposes its sequences as pairs of iterators. It happens frequently that two sequences of doubles have been calculated for some purpose, and then the sequence consisting of the quotients of the respective values is needed. Storing the quotients in a third sequence would clearly be a colossally dumb decision in terms of time-space tradeoff. Instead, the math engine exposes a combining iterator that parallel-iterates over the two given sequences and, upon dereferencing, returns the quotient of the two values at its current position. Many more situations exist in this software where a simple arithmetic expression is calculated on the fly from two or more sequences of numbers. Anectdotal Background ===================== We started working on the software mentioned above in 1997, and we have been using the STL and generic programming paradigms from Day 1. We have used "smart iterators" as early as 1998. Back then, the idea seemed so new to me that I wrote an article about it in CUJ (CUJ September 1998). Two years later, we had accumulated so many "smart," or "custom" iterators that my friend and colleague Chris Baus and I wrote antother article about it for the 2000 C++ Template Workshop (http://oonumerics.org/tmpw00). Needless to say, from today's point of view, our smart iterators were all spit'n duct tape. It was of course the boost::iterator_adaptor (which by the way was first presented at the 2001 C++ Template Workshop, http://oonumerics.org/tmpw00) that provided the proper framework for doing this. I recently noticed that the ready-to-use boost now provide almost everything that we use, with the exception of the combining iterator. But this is a very important one for us, hence the proposed submission. Please comment. Thomas Becker Zephyr Associates, Inc. Zephyr Cove, NV __________________________________________________ Do you Yahoo!? Yahoo! Platinum - Watch CBS' NCAA March Madness, live on your desktop! http://platinum.yahoo.com _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
