-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of David Abrahams
PY_DEFINE_CONSTANTS_NO_EXPANSION((foo)(bar) BOOST_PP_INTERCEPT_)
The trick here is to get the sequence inside the machinery in a way that allows the machinery to prevent it from expanding. That's the trailing 'INTERCEPT_ and the 'seq ## 0'. From there, it can be immediately processed with custom sequential iteration to make a new sequence with a argument/string pairs.
According to http://www.boost.org/libs/preprocessor/doc/ref/intercept.html there's no trailing underscore. Am I missing something?
I'm cheating a bit. INTERCEPT expands to INTERCEPT_, which expands to nothing when a number is pasted to the tail. In this context, INTERCEPT won't expand in time, so you'd get INTERCEPT0, which won't expand at all (because it isn't a macro), rather than INTERCEPT_0 (which will). The library is not designed to allow for the sort of timing required for delayed invocation. Rather, it is intentionally designed (in most cases) to allow arguments to expand on input. Plus, not only is it impossible to do portably, it can quickly become a vertical dependency nightmare because macros start expanding in contexts that they weren't designed to expand in. I.e. the implementation details of macros, in particular, become subject to the environment context (i.e. what macros are currently disabled). Chaos has limited support for this type of thing, but it really is limited. What you can do in these contexts becomes severally restricted with respect to what other library primitives you can use. One thing that you can do safely, relative to expansion timing, is delay invocation all the way through some other macro (several ways to do this). But it is dangerous to make something expand some arbitrary number of steps into another macro expansion. Regards, Paul Mensonides