WHAT: ===== An instantiation of "begin<T>::type" fails to compile if T is an MPL Integral Constant. 'begin' is supposed to return 'void_' for all types that do not model the MPL Sequence concept. The bug also causes 'is_sequence' to fail. FILES: ====== - begin_end_impl.hpp.patch changes needed to make things work like documented - is_sequence.cpp.patch inclusion of the problematic case in the test suite diffed against: CVS HEAD TESTED WITH: ============ - MSVC 8.0 - MSVC 7.1 - GCC 3.4.2 Index: boost/mpl/aux_/begin_end_impl.hpp =================================================================== RCS file: /cvsroot/boost/boost/boost/mpl/aux_/begin_end_impl.hpp,v retrieving revision 1.8 diff -u -r1.8 begin_end_impl.hpp --- boost/mpl/aux_/begin_end_impl.hpp 2 Sep 2004 15:40:43 -0000 1.8 +++ boost/mpl/aux_/begin_end_impl.hpp 15 May 2006 23:22:17 -0000 @@ -17,12 +17,30 @@ #include <boost/mpl/begin_end_fwd.hpp> #include <boost/mpl/sequence_tag_fwd.hpp> #include <boost/mpl/void.hpp> +#include <boost/mpl/eval_if.hpp> +#include <boost/mpl/aux_/has_begin.hpp> #include <boost/mpl/aux_/na.hpp> #include <boost/mpl/aux_/traits_lambda_spec.hpp> #include <boost/mpl/aux_/config/eti.hpp> namespace boost { namespace mpl { + +namespace aux { + +template< typename Sequence > +struct begin_type +{ + typedef typename Sequence::begin type; +}; +template< typename Sequence > +struct end_type +{ + typedef typename Sequence::end type; +}; + +} + // default implementation; conrete sequences might override it by // specializing either the 'begin_impl/end_impl' or the primary // 'begin/end' templates @@ -32,7 +50,8 @@ { template< typename Sequence > struct apply { - typedef typename Sequence::begin type; + typedef typename eval_if<aux::has_begin<Sequence, true_>, + aux::begin_type<Sequence>, void_>::type type; }; }; @@ -41,7 +60,8 @@ { template< typename Sequence > struct apply { - typedef typename Sequence::end type; + typedef typename eval_if<aux::has_begin<Sequence, true_>, + aux::end_type<Sequence>, void_>::type type; }; }; Index: libs/mpl/test/is_sequence.cpp =================================================================== RCS file: /cvsroot/boost/boost/libs/mpl/test/is_sequence.cpp,v retrieving revision 1.5 diff -u -r1.5 is_sequence.cpp --- libs/mpl/test/is_sequence.cpp 2 Sep 2004 15:41:35 -0000 1.5 +++ libs/mpl/test/is_sequence.cpp 15 May 2006 22:55:40 -0000 @@ -12,6 +12,7 @@ // $Revision: 1.5 $ #include <boost/mpl/is_sequence.hpp> +#include <boost/mpl/int.hpp> #include <boost/mpl/list.hpp> #include <boost/mpl/vector.hpp> #include <boost/mpl/range_c.hpp> @@ -25,6 +26,7 @@ MPL_TEST_CASE() { MPL_ASSERT_NOT(( is_sequence< std_vector<int> > )); + MPL_ASSERT_NOT(( is_sequence< int_<0> > )); MPL_ASSERT_NOT(( is_sequence< int > )); MPL_ASSERT_NOT(( is_sequence< int& > )); MPL_ASSERT_NOT(( is_sequence< UDT > ));