Re: [Boost-users] [preprocessor] concatenating values to create typedefpermutations

14 Jun 2006


      ...
-----Original Message-----
From: boost-users-bounces@lists.boost.org 
[mailto:boost-users-bounces@lists.boost.org] On Behalf Of Chris Weed
...
Hi,
I am trying to use the preprocessor iteration ability to 
create typedef permutations.
I want to do something like use the following set of types
TYPE1: char int float
TYPE2: char int float double
to generate permutations of MyClass such as
typedef MyClass Mycc;
typedef MyClass Myci;
typedef MyClass Mycf;
...
Creating the permutations is easy, but you can't automatically extract the first
character of an identifier (e.g. 'char' is an identifier to the preprocessor) to
generate the "unique" typedef name.  The best that you can do is either pass it
along as a separate field (what the code below does) or provide a way to obtain
it through some kind of type registration.

Regards,
Paul Mensonides

#include 
#include 
#include 
#include 
#include 

#define A(r, product) \
    typedef MyClass< \
        BOOST_PP_SEQ_ENUM(BOOST_PP_SEQ_TRANSFORM(B, 1, product)) \
    > \
    BOOST_PP_SEQ_CAT((My) BOOST_PP_SEQ_TRANSFORM(B, 0, product)); \
    /**/
#define B(s, i, elem) BOOST_PP_SEQ_ELEM(i, elem)

#define TYPE(alpha, id) ((alpha)(id))

BOOST_PP_SEQ_FOR_EACH_PRODUCT(
    A,
    ( TYPE(c, char) TYPE(i, int) TYPE(f, float) )
    ( TYPE(c, char) TYPE(i, int) TYPE(f, float) TYPE(d, double) )
)

#undef A
#undef B
#undef TYPE