...one of the most highly
regarded and expertly designed C++ library projects in the
world. — Herb Sutter and Andrei
VMD has the ability to retrieve the type of any data which it can parse, which means any VMD sequence. The macro to do this is called BOOST_VMD_GET_TYPE and it takes a single required variadic parameter, which is a VMD sequence. Since a VMD sequence is any data which VMD can parse the BOOST_VMD_GET_TYPE macro works with any VMD data.
It returns one of the types previously discussed when introducing v-types as an identifier subset. As explained previously in that topic a v-type is fully recognized by VMD macros and can be part of a sequence and passed as VMD data just like all the other data types VMD recognizes.
When BOOST_VMD_GET_TYPE returns the type of data it returns by default the most specific type that the data can be. This means that non-empty lists and arrays are returned as such, not as tuples, and numbers and types and empty lists are returned as such, not as identifiers.
#include <boost/vmd/get_type.hpp> #define BOOST_VMD_REGISTER_ANID (ANID) #define SEQUENCE_EMPTY #define SEQUENCE_MULTI (1,2,3) 88 #define SEQUENCE1 (3,(1,2,3)) #define SEQUENCE2 ANID #define SEQUENCE3 (1,(2,(3,BOOST_PP_NIL))) #define SEQUENCE4 1 #define SEQUENCE5 (1)(2)(3) #define SEQUENCE6 (1,2,3) #define SEQUENCE7 BOOST_VMD_TYPE_NUMBER BOOST_VMD_GET_TYPE(SEQUENCE_EMPTY) will return BOOST_VMD_TYPE_EMPTY BOOST_VMD_GET_TYPE(SEQUENCE_MULTI) will return BOOST_VMD_TYPE_SEQUENCE BOOST_VMD_GET_TYPE(SEQUENCE1) will return BOOST_VMD_TYPE_ARRAY BOOST_VMD_GET_TYPE(SEQUENCE2) will return BOOST_VMD_TYPE_IDENTIFIER BOOST_VMD_GET_TYPE(SEQUENCE3) will return BOOST_VMD_TYPE_LIST BOOST_VMD_GET_TYPE(SEQUENCE4) will return BOOST_VMD_TYPE_NUMBER BOOST_VMD_GET_TYPE(SEQUENCE5) will return BOOST_VMD_TYPE_SEQ BOOST_VMD_GET_TYPE(SEQUENCE6) will return BOOST_VMD_TYPE_TUPLE BOOST_VMD_GET_TYPE(SEQUENCE7) will return BOOST_VMD_TYPE_TYPE
You can use the general header file:
or you can use the individual header file:
for the BOOST_VMD_GET_TYPE macro.