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 01:45:30

On Thu, Oct 14, 2010 at 11:41 PM, alfC <alfredo.correa_at_[hidden]> wrote:
>
>
> On Oct 14, 10:30Â pm, OvermindDL1 <overmind..._at_[hidden]> wrote:
>> On Thu, Oct 14, 2010 at 11:09 PM, alfC <alfredo.cor..._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:
>> Â  // include fusion here
>>
>> Â  int f(double d , int i , std::string s){
>> Â  Â  ...bla bla ...
>> Â  }
>>
>> Â  int main(void) {
>> Â  Â  boost::fusion::vector<double,int,std::string myVec(3.14, 42,
>> "Hello World!");
>> Â  Â  return boost::fusion::invoke(&f, myVec);
>> Â  }
>
> cool.
> one question: Â 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/functional/concepts/callable.html

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).