[Boost-users] [fusion] proposal BOOST_FUSION_ADAPT_FUNCTION, BOOST_FUSION_DEFINE_FUNCTION, etc

Subject: [Boost-users] [fusion] proposal BOOST_FUSION_ADAPT_FUNCTION, BOOST_FUSION_DEFINE_FUNCTION, etc
From: alfC (alfredo.correa_at_[hidden])
Date: 2010-10-15 01:09:44

Hi,

 I am using Boost.Fusion lately. Sometimes one has a function with
several parameters,

int f(double d , int i , std::string s){
 ...bla bla ...
}

the logic of the program says that sometimes that same funcion will be
called by generic code and in such case it is better if "f" where
defined as taking a fusion::vector as argument.

int f(fusion::vector<double, int, std::string>) // another function,
could be an overload even

since there is only one why to define this adaptor function, e.g.
int f(fusion::vector<double, int, std::string> x){
  return f(at_c<0>(x), at_c<1>(x), at_c<2>(x));\
}

and it is pretty mechanical. I was wondering if it would be a good
idea to have, with consistency with the  BOOST_FUSION_ADAPT_STRUCT,
something called BOOST_FUSION_ADAPT_FUNCTION

BOOST_FUSION_ADAPT_FUNCTION(
    int, f,
    double,
    int,
    std::string
)
(or something like that)
that defines the second / fusion-compatible version of f.

It could be even a

BOOST_FUSION_DEFINE_FUNCTION(
    int, f,
    (double, d),
    (int, i),
    (std::string, s),
    ( ... code using variables d, i, s or at_key<d_>, at_key<i_>,
at_key<s_> ...  )
)

that defines simultaneously the raw-C function, f(double, int, string)
*and* the fusion friendly version f(vector<...>).
I could probably program these macro for specific cases but not a
general one since I don't know enough macro syntax to make it work.

Do you think it is a good idea or it is already doable with existing
Fusion features?

Thank you,
Alfredo