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

Subject: Re: [Boost-users] [fusion] proposal BOOST_FUSION_ADAPT_FUNCTION, BOOST_FUSION_DEFINE_FUNCTION, etc
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2010-10-15 01:30:28

On Thu, Oct 14, 2010 at 11:09 PM, alfC <alfredo.correa_at_[hidden]> wrote:
> Hi,
>
> Â I am using Boost.Fusion lately. Sometimes one has a function with
> several parameters,
>
> int f(double d , int i , std::string s){
> Â ...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){
> Â 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(
> Â  Â int, f,
> Â  Â double,
> Â  Â int,
> Â  Â std::string
> )
> (or something like that)
> that defines the second / fusion-compatible version of f.
>
> It could be even a
>
> BOOST_FUSION_DEFINE_FUNCTION(
> Â  Â int, f,
> Â  Â (double, d),
> Â  Â (int, i),
> Â  Â (std::string, s),
> Â  Â ( ... code using variables d, i, s or at_key<d_>, at_key<i_>,
> at_key<s_> ... Â )
> )
>
> 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?

It should already be doable, given example:
  // include fusion here

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

  int main(void) {
    boost::fusion::vector<double,int,std::string myVec(3.14, 42,
"Hello World!");
    return boost::fusion::invoke(&f, myVec);
  }