Just one comment: From: Sean Parent
Consider -
to_lower(first, last, output)
How do you handle that with just a forward iterator? You need to read a whole word before you can decide whether "SS" should be "ß" or "ss" in the output. (I suppose you could read the word into an internal buffer - but that seems extreme).
such transformations can work with any encoding (you can uppercase UTF-8 into UTF-32). They can't work in-situ (but I don't think to_upper or to_lower really can work in-situ - certainly not in UTF-8 and probably not in UTF-16, and I believe there are some multi- character forms that even break in UTF-32...).
It is ß -> SS that break in-situ conversion! -- Martin Bonner Martin.Bonner@Pitechnology.com Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ, ENGLAND Tel: +44 (0)1223 203894