[Boost-users] [Phoenix]

Subject: [Boost-users] [Phoenix]
From: James Knight (james.nate.knight_at_[hidden])
Date: 2009-11-24 14:09:49

I'm having a problem using Boost.Phoenix.  I'm currently building against
Boost 1.41 using gcc 4.3.2.

I've simplified my use case quite a bit, so please forgive the obtuseness of
the example.  The following code fails to compile:

~~~~~~~~~~~~~~~~~~~~

#include <boost/fusion/include/std_pair.hpp>
#include <boost/spirit/home/phoenix/core/argument.hpp>
#include <boost/spirit/home/phoenix/fusion.hpp>
#include <boost/spirit/home/phoenix/operator.hpp>

#include
<vector>

#include
<map>
#include <algorithm>

namespace phx = boost::phoenix;
using namespace phx::arg_names;
using phx::at_c;
using std::map;
using std::multimap;
using std::vector;

int main()
{

    typedef map<vector<char>,int>
char_int_map_t;
    typedef multimap<int,char_int_map_t::iterator>
int_iter_map_t;
    typedef map<vector<char>, char_int_map_t::iterator>
char_iter_map_t;

    int int_key =
5;

    char_int_map_t
int_map;

    int_iter_map_t
int_iter_map;

    char_iter_map_t char_iter_map1,
char_iter_map_t2;

    int_iter_map_t::iterator
start,stop;

std::pair<int_iter_map_t::iterator,int_iter_map_t::iterator>

        er = int_iter_map.equal_range(int_key);

    std::set_intersection(
        char_iter_map1.begin(), char_iter_map1.end(),
        er.first,er.second,
        inserter(char_iter_map_t2,char_iter_map_t2.begin()),
        phx::at_c<0>(arg1) < phx::at_c<0>(*phx::at_c<1>(arg2))    // <-
COMPILE FAILURE
    );
}

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the information I can offer,

1) When the key in char_int_map_t and char_iter_map_t is a char rather than
a vector<char> this compiles without problems.
2) The gcc error shows that the arguments to the generated function object
are being switched (I think, see below)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
.../comparison.hpp:29:5: error: no match for ‘operator<’ in
‘result_of_less<const int&, const vector<char>&>::x < result_of_less<const
int&, const vector<char>&>::y’
.../comparison.hpp: In instantiation of ‘const int result_of_less<const
int&, const vector<char>&>::index’:
.../comparison.hpp:29:   instantiated from ‘result_of_less<const int&, const
vector<char>&>’
.../mpl/eval_if.hpp:38:   instantiated from ‘eval_if<or_<is_actor<const
int&>, is_actor<const vector<char>&>, mpl_::bool_<false>,
mpl_::bool_<false>, mpl_::bool_<false> >, re_curry<less_eval, const int&,
const vector<char>&>, result_of_less<const int&, const vector<char,
allocator<char> >&> >’
.../comparison.hpp:39:   instantiated from ‘

boost::phoenix::less_eval::result<
    boost::phoenix::basic_environment<

std::pair<
// This should be the second argument, no?
            const
int,

            std::_Rb_tree_iterator<std::pair<const std::vector<char,
std::allocator<char> >, int>>
        >,
        std::pair<
            const std::vector< char, std::allocator<char> >,
            std::_Rb_tree_iterator<std::pair<const std::vector<char,
std::allocator<char> >, int>>
        >
    >,
    boost::phoenix::composite<
        boost::phoenix::at_eval<0>,
        boost::fusion::vector<
            boost::phoenix::argument<0>
        >
    >,
    boost::phoenix::composite<
        boost::phoenix::at_eval<0>,
        boost::fusion::vector<
            boost::phoenix::composite<
                boost::phoenix::dereference_eval,
                boost::fusion::vector<
                    boost::phoenix::composite<
                        boost::phoenix::at_eval<1>,
                        boost::fusion::vector<
                            boost::phoenix::argument<1>
                        >
                    >
                >
            >
        >
    >
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

3) Finally, if I use the expression

    phx::at_c<0>(arg1) < *phx::at_c<1>(arg2)

the code still fails to compile (obviously), but does seem to get the
arguments in the correct order.

Any ideas?

Thanks
Nate