Re: [Boost-users] Fusion transform question

19 Jul 2008

      AMDG

Joel FALCOU wrote:
...
I started porting over some old codes that used hand-made 
MPL<->concrete object code to Fusion.
I'm currently trying to have the following to work with no results so 
far :
Strange as it may seem, fusion::transform is not
the right tool in this case, mpl::transform is what you
want.  fusion::transform is lazy.  It returns a transform_view.
mpl::transform works because fusion sequences /are/ mpl
sequences.  The default behavior of mpl::transform
is to preserve the input sequence type.  i.e.  transforming
an mpl::vector gives an mpl::vector, transforming an mpl::list
gives an mpl::list, and transforming a fusion::vector gives
a fusion::vector.

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

namespace bf = boost::fusion;
namespace mpl = boost::mpl;

struct make_arg {
    template<class T> struct apply {
        typedef typename boost::add_reference<
            typename boost::add_const<T>::type
        >::type type;
    };
};

template<class Args> struct tree {
    typedef Args    children;
    typedef typename mpl::transform::type contents;

    template tree( const T0& t0 , const T1& t1 )
      : mArgs(t0, t1) {}

    template
    typename bf::result_of::at_c::type get() const {
        return bf::at_c<I>(mArgs);
    }
    contents mArgs;
};

int main() {
    int k = 3;
    float u = 7.2f;
    tree< bf::vector > tree(k, u);
}

In Christ,
Steven Watanabe