-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Tobias Schwinger
Take a look at 'cat.hpp'. [...]
Aha - interesting! I've been wondering what this code does before... So it's about stabilizing the expansion order.
The EDG configuration, in case you're wondering, isn't working around any semantic problems or bugs. Older versions of the EDG preprocessor--like the one in Comeau's current release--have a significant flaw that prevents Chaos from working (fixed in newer versions). However, the Boost pp-lib doesn't exploit techniques related to it, and so the EDG configuration isn't doing a bug workaround per se. Rather, it is a speed workaround--and a strange one. Basically, it just adds delays. E.g. instead of #define A(x) B(C(x)) ...it does... #define A(x) A2(x) #define A2(x) B(C(x)) This "extra" macro, used consistently in places where arguments contain macro expansions drastically improves the speed of that preprocessor (not that the improves the speed enough...). I don't know exactly why, but apparently has something to do with the data structures that EDG was using during macro expansion. The more you know... :) Regards, Paul Mensonides