I am going to use our wonderful Preprocessor library to generate a
metafunction that basically looks like this:
template<
int C0, int C1, ..., int Cn
>
struct max_arity
{
static int const value = Cn > 0 ? Cn : ( Cn-1 > 0 ? Cn-1 :
... ( C1 > 0 ? C1 : ( C0 > 0 ? C0 : -1 ) ) )
;
};
So here's what I came up with:
template<
BOOST_PP_ENUM_PARAMS(BOOST_MPL_METAFUNCTION_MAX_ARITY, int C)
>
struct max_arity
{
BOOST_STATIC_CONSTANT(int,
value = BOOST_PP_LIST_FOLD_LEFT(
AUX_MAX_ARITY_OP
, -1
, (0, (1, (2, (3, (4, BOOST_PP_NIL)))))
)
);
};
I love everything about it except for the "(0, (1, (2, (3, (4,
BOOST_PP_NIL)))))" part. I would like the above to become something along
these lines:
value = BOOST_PP_RANGE_FOLD_LEFT(
AUX_MAX_ARITY_OP
, -1
, BOOST_PP_RANGE(0, 4)
)
or, better yet,
value = BOOST_PP_FOLD_LEFT(
AUX_MAX_ARITY_OP
, -1
, BOOST_PP_RANGE(0, 4)
)
where 'BOOST_PP_FOLD_LEFT' is a generic algorithm that can be used on all PP
sequences.
How hard would it be to have something like this?
I suppose it's possible to generate the code I need using BOOST_PP_WHILE,
but IMO that solution wouldn't be as conceptually nice and intuitive as the
above.
Aleksey
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