Subject: Re: [boost] Help with Boost Preprocessor
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-08-29 21:34:41
AMDG
Emil Dotchevski wrote:
> Let's say I have a class template functor like this:
>
> struct
> func
> {
> typedef void result_type;
>
> template <class A1,class A2,class A3>
> void
> operator()( A1, A2, A3, int x )
> {
> }
> };
>
> Given a list of types, I want the function instantiated and called for
> all permutations of the types in the list; the additional argument(s),
> x, just need to be forwarded the same for all instances.
>
> Actually I got it working, see http://codepad.org/tnYTy9Iw.
>
> I don't think that my solution is very good though. First, it has some
> run-time overhead due to the use of boost::bind in fwd1 and fwd2 (see
> link above.) Second, I'd like the macro that defines the type list not
> to be hard-coded in fwd1 and fwd2.
>
> Is this possible?
>
How does this work
#include <boost/preprocessor/seq/for_each_product.hpp>
#include <boost/preprocessor/seq/transform.hpp>
#include <boost/preprocessor/seq/enum.hpp>
#include <iostream>
struct
func
{
typedef void result_type;
template <class A1,class A2,class A3>
void
operator()( A1, A2, A3, int x )
{ std::cout <<
typeid(A1).name() << ',' <<
typeid(A2).name() << ',' <<
typeid(A3).name() << ',' <<
x << '\n';
}
};
template<class T>
T make() { return T(); }
#define CALL_FUNC(r, args) func()(BOOST_PP_SEQ_ENUM(args), x);
#define MAKE_OBJECT(s, data, elem) make<elem>()
#define FUNC_II(types) \
BOOST_PP_SEQ_FOR_EACH_PRODUCT(CALL_FUNC, (types)(types)(types))
#define FUNC_I(types) FUNC_II(types)
#define FUNC(types, arg) \
if(true) { \
int x = arg; \
FUNC_I(BOOST_PP_SEQ_TRANSFORM(MAKE_OBJECT, ~, types)) \
} else ((void)0)
int main() {
FUNC((int)(long), 42);
}
In Christ,
Steven Watanabe