[Boost-bugs] [Boost C++ Libraries] #6961: problem with list_c et.all

Subject: [Boost-bugs] [Boost C++ Libraries] #6961: problem with list_c et.all
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-06-03 17:55:46

#6961: problem with list_c et.all
------------------------------+---------------------------------------------
 Reporter:  ramey             |       Owner:  agurtovoy
     Type:  Bugs              |      Status:  new      
Milestone:  To Be Determined  |   Component:  mpl      
  Version:  Boost 1.49.0      |    Severity:  Problem  
 Keywords:                    |  
------------------------------+---------------------------------------------
 The documentation for list_c states that it is a model of Front Extensible
 Sequence.

 But some simple testing suggests otherwise.  Here is my test program:


 {{{
 #include "../include/multi_precision.hpp"

 //#include <boost/mpl/shift_right.hpp>
 //#include <boost/mpl/integral_c.hpp>
 //#include <boost/cstdint.hpp>

 #include <boost/mpl/list.hpp>
 #include <boost/mpl/list_c.hpp>
 #include <boost/mpl/push_front.hpp>
 #include <boost/mpl/front.hpp>
 #include <boost/mpl/int.hpp>
 #include <boost/mpl/integral_c.hpp>

 #include <boost/mpl/print.hpp>

 namespace boost {
 namespace mpl {

 print<
     list_c<int,
        22,
        64
     >
 > x8;

 print<
     front<
         list_c<int,
            22,
            64
         >
     >::type
 > x7;

 print<
     push_front<
         list_c<int,
             22,
             64
         >,
         integral_c<int, 33>
     >::type
 > x6;


 }}}

 which produces the following output on my VC 9.0 compiler


 {{{
 1>------ Build started: Project: test_interval, Configuration: Debug Win32
 ------
 1>Compiling...
 1>test_multi_precision.cpp
 1>c:\boostrelease\boost\mpl\print.hpp(51) : warning C4308: negative
 integral constant converted to unsigned type
 1>        c:\projects\boost
 projects\mpl\tests\test_multi_precision.cpp(24) : see reference to class
 template instantiation 'boost::mpl::print<T>' being compiled
 1>        with
 1>        [
 1>            T=boost::mpl::list_c<int,22,64>
 1>        ]
 1>c:\boostrelease\boost\mpl\print.hpp(51) : warning C4308: negative
 integral constant converted to unsigned type
 1>        c:\projects\boost
 projects\mpl\tests\test_multi_precision.cpp(33) : see reference to class
 template instantiation 'boost::mpl::print<T>' being compiled
 1>        with
 1>        [
 1>            T=boost::mpl::integral_c<int,22>
 1>        ]
 1>c:\boostrelease\boost\mpl\print.hpp(51) : warning C4308: negative
 integral constant converted to unsigned type
 1>        c:\projects\boost
 projects\mpl\tests\test_multi_precision.cpp(44) : see reference to class
 template instantiation 'boost::mpl::print<T>' being compiled
 1>        with
 1>        [
 1>
 T=boost::mpl::l_item<boost::mpl::long_<3>,boost::mpl::integral_c<int,33>,boost::mpl::list2_c<int,22,64>>
 1>        ]

 }}}

 What I hope to see for the third test is:

 {{{
 T=boost::mpl::list_c<int,33, 22,64>
 }}}

 If I use

 {{{
 print<
     push_front<
         list_c<int,
             22,
             64
         >,
         33
     >::type
 > x5;
 }}}

 But this fails to compile at all.

 To me, the list_c implementation is misconceived. Maybe the following
 should result

 {{{
 print<
     list_c<int,
        22,
        64
     >::type // note the ::type to make it a metafunction
 > x8;
 }}}

 to return

 {{{
 T=boost::mpl::list<boost::mpl::integral_c<int,
 22>,boost::mpl::integral_c<int, 64> >
 }}}

 Of course the same observations would apply to vector_c, etc.

 Robert Ramey

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6961>
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