Re: [Boost-users] Tuples: Can someone help me generalize this?

17 Sep 2008

      AMDG

Derrick Hathaway wrote:
...
Thank you, Sir, for your quick response. I just got around to testing 
it, and I've run into a snag. a fusion::vector is larger than the sum 
of it's parts, and I would like something that is not. In other words:
sizeof(vector) != sizeof(float) + sizeof(float)
Please create a trac ticket for this.  It looks like EBCO is not working 
properly,
because the compiler refuses to allocate two instances of 
boost::fusion::sequence_root
at the same address.
...
A tuple seems to fit, as I described earlier, but I'm not sure how to 
generalize this. I've thought that there might be a way to generalize 
a tuple to provide an interface like my_tuple using the cons. 
Any thoughts?
Unfortunately cons doesn't quite work because it it doesn't have the
constructor you want.

You can use the general mpl::inserter to create a specialization of
tuple.

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

#include <iostream>

template
struct tuple_push_front;

template
struct tuple_push_front, T> {
    typedef boost::tuple type;
};

// create a sequence of 5 elements
typedef boost::mpl::range_c range;
// convert all the elements to float and make the result a fusion vector.
typedef boost::mpl::transform,
        tuple_push_front
    >
...
::type tuple_type;
int main() {
   tuple_type t(0, 1, 2, 3, 4);
   std::cout << typeid(tuple_type).name() << std::endl;
}

In Christ,
Steven Watanabe