Re: [Boost-users] [fusion] memory layout of fusion::vector vs boost::tuple/boost::array

Subject: Re: [Boost-users] [fusion] memory layout of fusion::vector vs boost::tuple/boost::array
From: alfC (alfredo.correa_at_[hidden])
Date: 2010-10-08 02:59:01

On Oct 7, 5:13 pm, OvermindDL1 <overmind..._at_[hidden]> wrote:
> On Thu, Oct 7, 2010 at 5:42 PM, Alfredo Correa <alfredo.cor..._at_[hidden]> wrote:
> > On Thu, Oct 7, 2010 at 3:33 PM, OvermindDL1 <overmind..._at_[hidden]> wrote:
> >> You do know that based on this:
>
> >>  http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html/fusion/adap...
> >> boost::array is already adapted as a fusion container and can be used
> >> directly, as soon as you include the proper hpp that is?
>
> > yes, thank you, that what I wrote in my last post . I can make this work
>
> > #include <boost/fusion/adapted/boost_array.hpp>
> > #include <boost/fusion/include/boost_array.hpp>
> > ...
> > boost::array<double, 3> boostarr={{1.0, 2.1, 3.2}};
> > vector<double, double, double> fusionvec(boostarr); //now works
>
> Ah, heh, got lost in the noise and I missed it.
>
> On Thu, Oct 7, 2010 at 5:42 PM, Alfredo Correa <alfredo.cor..._at_[hidden]> wrote:
> > I still can't do the other way around:
>
> > boost::array<double, 3> boostarr2(fusionvec); //doesn't work
> > ideas?
>
> I know that would not work because that is still a 'custom' type as
> far as fusion is concerned, and only free functions can work on it, a
> constructor is obviously not a free function, so you need to write a
> free function to do it (probably called 'copy', probably using
> fusion's foreach to copy each element one to the other, should be
> pretty well optimized out thanks to the template-magic).

no luck. I can't make it work. First I tried with "for_each" and
didn't manage to put together the code because I need to copy one
sequence from the other and the for_each doesn't keep track of the
index. So I tried with "transform", the code compiles but does nothing
to the array.

        boost::array<double, 3> ba0;
        boost::fusion::transform(ba0, bfv1, copy());

where
struct copy{
        typedef void result_type;
        void operator()(double& lhs, double const& rhs) const{
                lhs = rhs;
        }
};

ba0 is still undefined after running this.

Obviously I am getting Boost.Fusion wrong.

Thanks,
Alfredo

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