Re: [Boost-users] [MPL] mpl::at for AssociativeSequence

Subject: Re: [Boost-users] [MPL] mpl::at for AssociativeSequence
From: Gordon Woodhull (gordon_at_[hidden])
Date: 2012-06-12 13:33:18

https://svn.boost.org/trac/boost/ticket/3982

On Jun 12, 2012, at 12:11 PM, dariomt_at_[hidden] wrote:

> Hi list,
> 
> I'm trying to use the version of mpl::at with three template parameters, as specified here (http://www.boost.org/doc/libs/1_46_0/libs/mpl/doc/refmanual/at.html)
> 
> But I'm getting a compiler error saying 'boost::mpl::at' : too many template arguments.
> 
> What am I doing wrong?
> 
> 
> #include <boost/mpl/map.hpp>
> #include <boost/mpl/at.hpp>
> #include <boost/mpl/size.hpp>
> #include <boost/mpl/empty.hpp>
> #include <boost/type_traits/is_same.hpp>
> 
> using namespace boost;
> using namespace boost::mpl;
> 
> typedef map<
>       pair<int,unsigned>
>     , pair<char,unsigned char>
>     , pair<long_<5>,char[17]>
>     , pair<int[42],bool>
>     > m;
> 
> BOOST_MPL_ASSERT_RELATION( size<m>::value, ==, 4 );
> BOOST_MPL_ASSERT_NOT(( empty<m> ));
> 
> BOOST_MPL_ASSERT(( is_same< at<m,int>::type, unsigned > ));
> BOOST_MPL_ASSERT(( is_same< at<m,long_<5> >::type, char[17] > ));
> BOOST_MPL_ASSERT(( is_same< at<m,int[42]>::type, bool > ));
> BOOST_MPL_ASSERT(( is_same< at<m,long>::type, void_ > ));
> 
> BOOST_MPL_ASSERT(( is_same< at<m,long,void_>::type, void_ > )); // fails!
> 
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