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

15 Oct 2010

      On Oct 14, 10:45 pm, OvermindDL1  wrote:
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On Thu, Oct 14, 2010 at 11:41 PM, alfC  wrote:
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On Oct 14, 10:30 pm, OvermindDL1  wrote:
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On Thu, Oct 14, 2010 at 11:09 PM, alfC  wrote:
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Hi,
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 I am using Boost.Fusion lately. Sometimes one has a function with
several parameters,
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int f(double d , int i , std::string s){
 ...bla bla ...
}
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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.
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int f(fusion::vector) // another function,
could be an overload even
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since there is only one why to define this adaptor function, e.g.
int f(fusion::vector x){
 return f(at_c<0>(x), at_c<1>(x), at_c<2>(x));\
}
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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
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BOOST_FUSION_ADAPT_FUNCTION(
   int, f,
   double,
   int,
   std::string
)
(or something like that)
that defines the second / fusion-compatible version of f.
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It could be even a
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BOOST_FUSION_DEFINE_FUNCTION(
   int, f,
   (double, d),
   (int, i),
   (std::string, s),
   ( ... code using variables d, i, s or at_key, at_key,
at_key ...  )
)
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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.
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Do you think it is a good idea or it is already doable with existing
Fusion features?
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It should already be doable, given example:
  // include fusion here
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  int f(double d , int i , std::string s){
    ...bla bla ...
  }
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  int main(void) {
    boost::fusion::vector
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cool.
one question:  does it work for member functions as well?
It works for any thing that fulfills the Boost.Fusion callable concept
as outlined here:
 http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html/fusion/func...
So yes, it works for member functions (where the class instance it is
called from is the ***first entry in the fusion vector/list/whatever).****
that "first entry" feature is an annoyance for my application.

I have mostly function objects

class f_impl{
  double operator()( double, int, string ...);
}

f_impl f;

for which I would like to have a systematic way of
using it as

f( vector )

without having to add the f_impl at the beginning of the
fusion::vector

Thank you,
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