[boost] [regex] begin-/end-line need to be customizable via traits

From: Eric Niebler (eric_at_[hidden])
Date: 2005-07-31 00:21:03

I think there is a problem in the regex standardization proposal 
regarding the begin- and end-of-line assertions (^ and $). It seems that 
there is no way to customize their behavior via the traits. This is 
inconsistent with the word boundary assertion, which is implementable in 
terms of the word character class (\w). The author of a traits class 
should be able to specify which characters are line separators.

A simple fix would be to add a character class for line separator 
characters. Then, ^ and $ could be implemented in terms of 
lookup_classname and isctype, just as the word boundary assertion is.

This leaves out an important corner case, though: \r is a line separator 
only if it is not immediately followed by a \n. I haven't yet come up 
with a traits interface that clean enough and general enough to satisfy. 
I'm open to suggestions.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com