[Boost-users] Inconsistent behavior of fusion::find with vector and adapted struct.

Subject: [Boost-users] Inconsistent behavior of fusion::find with vector and adapted struct.
From: Mike Tegtmeyer (tegtmeye_at_[hidden])
Date: 2009-08-05 17:02:29

I seem to have found an inconsistency in how fusion::find works with
fusion::vector and an adapted struct. Basically, attempting to find a
non-const type on a const vector with a non-const member works but requires
a const-member find for an adapted struct. (See code below). Is this
something that was just overlooked or there a technical reason for this
behavior. In any case is there some way to identify a adapted struct in the
general case (as apposed to the tag of the specific type) that can be used
for a workaround?
Thanks in advance,
Mike

#include <boost/fusion/adapted/struct/adapt_struct.hpp>

#include <boost/fusion/container/vector/vector.hpp>

#include <boost/fusion/algorithm/query/find.hpp>

#include <boost/type_traits.hpp>

#include <string>

#include <iostream>

namespace b = boost;

namespace bf = boost::fusion;

namespace demo

{

    struct employee

    {

        std::string name;

        int age;

    };

}

// demo::employee is now a Fusion sequence

BOOST_FUSION_ADAPT_STRUCT(

    demo::employee,

    (std::string, name)

    (int, age))

int main(void)

{

  typedef bf::vector<int,float> V1;

  // Find against non-const V1

  V1 v1(1,2.0);

  BOOST_MPL_ASSERT_NOT((
b::is_same<bf::result_of::find<V1,int>::type,bf::result_of::end<V1>::type>
));

  assert(*bf::find<int>(v1) == 1);

  // Find against const V1

  const V1 const_v1(3,4.0);

  BOOST_MPL_ASSERT_NOT(( b::is_same<bf::result_of::find<const V1,int
>::type,bf::result_of::end<const V1>::type> ));

  assert(*bf::find<int>(const_v1) == 3);

  // Find against non-const employee

  demo::employee e1 = {"Foo",18};

  BOOST_MPL_ASSERT_NOT((
b::is_same<bf::result_of::find<demo::employee,int>::type,bf::result_of::end<demo::employee>::type>
));

  assert(*bf::find<int>(e1) == 18);

  // Find against const employee

  const demo::employee const_e1 = {"Bar",21};

#if 0

  BOOST_MPL_ASSERT_NOT(( b::is_same<bf::result_of::find<constdemo::employee,
int>::type,bf::result_of::end<const demo::employee>::type> ));

  assert(*bf::find<int>(const_e1) == 21);

#else

  // note that the find key is a const int for this to work and is
inconsistent with fusion::vector

  BOOST_MPL_ASSERT_NOT(( b::is_same<bf::result_of::find<constdemo::employee,
const int>::type,bf::result_of::end<const demo::employee>::type> ));

  assert(*bf::find<const int>(const_e1) == 21);

#endif

  return 0;

}