Re: [boost] [mpl] mpl::c_str fails for mpl::push_back

9 Nov 2010

      ----- Original Message ----- 
From: "vicente.botet" <vicente.botet@wanadoo.fr>
To: <boost@lists.boost.org>
Sent: Monday, November 08, 2010 6:01 PM
Subject: Re: [boost] [mpl] mpl::c_str fails for mpl::push_back
...
I'll prepare a patch with the c_str parameter extension in a separated file, as it should not depend any more on mpl::string and could work with other sequences and the value_type trait in another file. Let me know if there is someting wrong.
Hi,

while trying to check c_str on set_c sequence I have found a behaviour that seems to a bug. With list_c, the following code works well, 

typedef mpl::list_c<char, 'a'> str_type;
typedef mpl::begin<str_type>::type i0;
typedef mpl::next<i0>::type i1;

but with set_c

typedef mpl::set_c<char, 'a'> str_type;
typedef mpl::begin<str_type>::type i0;
typedef mpl::next<i0>::type i1;

I get the following compile error on gcc

../../../boost/mpl/set/aux_/iterator.hpp: In instantiation of `boost::mpl::next<boost::mpl::s_iter<main()::str_type, boost::mpl::set0_c<char> > >':
../../../boost/mpl/eval_if.hpp:38:   instantiated from `boost::mpl::eval_if<boost::mpl::has_key<main()::str_type, mpl_::void_>, boost::mpl::identity<boost::mpl::s_iter<main()::str_type, boost::mpl::set0_c<char> > >, boost::mpl::next<boost::mpl::s_iter<main()::str_type, boost::mpl::set0_c<char> > > >'
../../../boost/mpl/set/aux_/iterator.hpp:38:   instantiated from `boost::mpl::s_iter_get<main()::str_type, boost::mpl::set0_c<char> >'
../../../boost/mpl/set/aux_/iterator.hpp:57:   instantiated from `boost::mpl::next<boost::mpl::s_iter<main()::str_type, boost::mpl::s_item<mpl_::integral_c<char, 'a'>, boost::mpl::set0_c<char> > > >'
c_str\c_str_pass.cpp:271:   instantiated from here

or this one with msvc

C:\cygwin\boost\v44\boost/mpl/set/aux_/iterator.hpp(56) : error C2039: 'base' : is not a member of 'boost::mpl::set0_c<T>'
        with
        [
            T=char
        ]
        C:\cygwin\boost\v44\boost/mpl/eval_if.hpp(41) : see reference to class template instantiation 'boost::mpl::next<T>' being compiled
        with
        [
            T=boost::mpl::s_iter<str_type,boost::mpl::set0_c<char>>
        ]
        C:\cygwin\boost\v44\boost/mpl/set/aux_/iterator.hpp(38) : see reference to class template instantiation 'boost::mpl::eval_if<C,F1,F2>' being compiled
        with
        [
            C=boost::mpl::has_key<str_type,boost::mpl::set0<>::item_type_>,
            F1=boost::mpl::identity<boost::mpl::s_iter<str_type,boost::mpl::set0_c<char>>>,
            F2=boost::mpl::next<boost::mpl::s_iter<str_type,boost::mpl::set0_c<char>>>
        ]
        C:\cygwin\boost\v44\boost/mpl/set/aux_/iterator.hpp(57) : see reference to class template instantiation 'boost::mpl::s_iter_get<Set,Tail>' being compiled
        with
        [
            Set=str_type,
            Tail=boost::mpl::set0_c<char>
        ]
        c_str\c_str_pass.cpp(271) : see reference to class template instantiation 'boost::mpl::next<T>' being compiled
        with
        [
            T=boost::mpl::s_iter<str_type,boost::mpl::s_item<boost::mpl::integral_c<char,97>,boost::mpl::set0_c<char>>>
        ]

BTW,

this works also

typedef mpl::set<mpl::char_<'a'> > str_type;
typedef mpl::begin<str_type>::type i0;
typedef mpl::next<i0>::type i1;

What is happening? Am I missing something evident or is this a real bug?

Best,
Vicente