On 6/30/2011 9:31 PM, Lorenzo Caminiti wrote:
On Wed, Jun 29, 2011 at 10:54 AM, Edward Diener<eldiener@tropicsoft.com> wrote:
Nonetheless macros using variadics to identify pp-lib data types on the fly might still be useful and I have already come up with a pretty good IS_TUPLE. Whether an IS_ARRAY, IS_LIST, or IS_SEQ is posible I shall see.
Useful indeed. I have implemented some sort of IS_TUPLE within Boost.Local.
It is certainly possible to do an IS_TUPLE when the possibilities are confined but it is not possible to do an IS_TUPLE which works in every case due to having to use IS_EMPTY to check that there is nothing beyond the end paren. If you think you have a fail-safe implementation if IS_TUPLE, feel free to share it. I will post an IS_TUPLE in my VMD library, with a note about the possible problem which could occur, but since I have my TTI library upcoming for review, I will wait until that review is ended. It is not possible to do an IS_ARRAY or an IS_LIST because it is not possible to check for a number or the presence of BOOST_PP_NIL. Using the well known concatenation technique to check for a particular token fails when the token tested can not be legally concatenated, ie. BOOST_PP_IS_1(+) fails with a programming error. It is possible to do an IS_SEQ based on IS_TUPLE, but with the same limitation IS_TUPLE has. I will post an IS_SEQ in my VMD library eventually also.
BOOST_LOCAL_PARAMS() uses it to accept both the follow syntaxes when variadics are present:
BOOST_LOCAL_PARAMS(int x, int& y) // (1) BOOST_LOCAL_PARAMS( (int x) (int& y) ) // (2)
Essentially (going by memory):
#if BOOST_VARIADICS_MACRO
#define BOOST_LOCAL_PARAMS(...) \ BOOST_PP_IIF(IS_TUPLE(__VA_ARGS__), \ BOOST_LOCAL_PARAMS_TUPLE_ /* for (1) */ \ , \ BOOST_LOCAL_PARAMS_SEQ_ /* for (2) */ \ )(__VA_ARGS__)
#else // variadics
#define BOOST_LOCAL_PARAMS(seq) BOOST_LOCAL_PARAMS_SEQ_(seq) // only (2) :(
#endif // variadics
I will probably end up putting any additions in my VMD library for the time being and if Paul decides that he wants them for pp-lib sometime in the future they will eventually go there.
I'd prefer to see IS_TUPLE (and possibly all IS_XXX) as part of these Boost.Preprocess variadics changes.
I do not control what Paul decides to add to pp-lib, but I am discussing these possibilities with him and he can decide the end result.