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

Subject: Re: [Boost-users] Inconsistent behavior of fusion::find with vector and adapted struct.
From: Mike Tegtmeyer (tegtmeye_at_[hidden])
Date: 2009-08-06 17:18:35

Thanks, added ticket 3322
Mike

On Wed, Aug 5, 2009 at 11:47 PM, Christopher Schmidt <
mr.chr.schmidt_at_[hidden]> wrote:

> I am pretty sure this is a bug. The cv-ness of a certain fusion type should
> not be relevant in this particular case.
>
> You can identify adapted structs by their fusion::struct_tag - tag.
>
> -C.
>
> Mike Tegtmeyer schrieb:
>
>> 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<const
>> demo::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<const
>> demo::employee,const int>::type,bf::result_of::end<const
>> demo::employee>::type> ));
>>
>>
>>  assert(*bf::find<const int>(const_e1) == 21);
>>
>> #endif
>>
>>
>>  return 0;
>>
>> }
>>
>>
>> ------------------------------------------------------------------------
>>
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>>
>
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