Daryle Walker wrote:
On 9/13/05 10:56 AM, "Eric Niebler" <eric@boost-consulting.com> wrote:
It's true that there is functional overlap between Regex and xpressive, but xpressive takes a much broader view of pattern matching. And just because one piece of this puzzle has been proposed for standardization doesn't mean that all innovation in this problem space must cease.
If xpressive gets accepted...
..could we factor stuff so common capabilities get to be in one set of code? (In other words, is xpressive is a super-set of Boost.Regex, and if so, can we change the implementation of Boost.Regex to use xpressive? What about any commonalities between these libraries and Spirit. Maybe we could have a grand unification of these three libraries some day, if appropriate. Of course, we could start a Regex and Spirit factoring now.)
xpressive is more like Spirit than Regex, and Joel and I have spent much time talking about unification possibilities. Our current thinking is that in the future, Spirit and xpressive will share a common core. In fact, I have already begun factoring out and generalizing large chunks of xpressive's meta-programming for reuse as a general expression template domain-specific embeded language compiler construction toolset (see boost/xpressive/detail/proto). In addition, xpressive already reuses Fusion, which is part of Spirit. Unification with Boost.Regex would be less straightforward. Look over my reply to Thomas Witt about the design of xpressive's basic_regex<> type: http://article.gmane.org/gmane.comp.lib.boost.devel/130973 xpressive's design goals led to a different interface and a different internal representation for the regex type. The interface chosen by Boost.Regex places some requirements on the implementation -- namely, that the compiled form of a regex much be iterator-neutral. xpressive's implementation is a poor fit for the Boost.Regex interface. IMO, it's best to leave Boost.Regex alone. Its implementation is a far better fit for its interface than xpressive would be. -- Eric Niebler Boost Consulting www.boost-consulting.com