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: Christopher Schmidt (mr.chr.schmidt_at_[hidden])
Date: 2009-08-05 23:47:07

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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