On 30 January 2010 06:57, joel falcou wrote:
Hicham Mouline wrote:
Hello,
struct params {
double field1;
double field2;
double field3;
double fiedl4;
};
I would like to generate all the types that hold any combination of the
members of params.
Can't you like generate a fusion vector out of combination enumeration ?
like having make_combo< params, vector_c<1,3,4> >
You'd want a map, at least. Consider:
template <typename T>
void foo(T const& x)
{
x.field3 *= 2;
}
How would you translate that to take a vector, if 'field3' could be in
different positions? But I've never used a fusion map so I don't know
how you'd go about that.
Here is are some macros to generate the necessary subsets. The main
loop could be implement using a fold, but as there can't be more than
8 iterations it seemed easier to hard code it.
Daniel
#include
#define SUBSETS(size, values) \
BOOST_PP_CAT(SUBSETS_, size) values
#define SUBSETS_1(a1) ((a1))
#define SUBSETS_2(a1,a2) \
SUBSETS_COMBINE(a2, SUBSETS_1(a1))
#define SUBSETS_3(a1,a2,a3) \
SUBSETS_COMBINE(a3, SUBSETS_2(a1,a2))
#define SUBSETS_4(a1,a2,a3,a4) \
SUBSETS_COMBINE(a4, SUBSETS_3(a1,a2,a3))
#define SUBSETS_5(a1,a2,a3,a4,a5) \
SUBSETS_COMBINE(a5, SUBSETS_4(a1,a2,a3,a4))
#define SUBSETS_6(a1,a2,a3,a4,a5,a6) \
SUBSETS_COMBINE(a6, SUBSETS_5(a1,a2,a3,a4,a5))
#define SUBSETS_7(a1,a2,a3,a4,a5,a6,a7) \
SUBSETS_COMBINE(a7, SUBSETS_6(a1,a2,a3,a4,a5,a6))
#define SUBSETS_8(a1,a2,a3,a4,a5,a6,a7,a8) \
SUBSETS_COMBINE(a8, SUBSETS_7(a1,a2,a3,a4,a5,a6,a7))
#define SUBSETS_COMBINE(x, seq_seq) \
seq_seq \
((x)) \
BOOST_PP_SEQ_FOR_EACH(SUBSETS_COMBINE_IMPL, x, seq_seq)
#define SUBSETS_COMBINE_IMPL(r, elem, seq) \
(seq (elem))
// Example of use:
SUBSETS(5, (field1, field2, field3, field4, field5))
