Markus Werle wrote:
using namespace boost::mpl;
typedef vector< pair< boost::is_pointer<_1>, _1 > , pair< boost::is_reference<_1>, boost::remove_reference<_1> > , pair< always<true_c>, boost::add_const<_1> > > switch_body;
typedef switch_< switch_body, char& >::type t1; typedef switch_< switch_body, int* >::type t2; typedef switch_< switch_body, int >::type t3;
BOOST_MPL_ASSERT_IS_SAME(t1, char); BOOST_MPL_ASSERT_IS_SAME(t2, int*); BOOST_MPL_ASSERT_IS_SAME(t3, int const);
[...]
What are the requirements for the struct some_condition<_1> to be used in such a switch body?
'some_condition' should be a metafunction (http://www.mywikinet.com/mpl/ref/Metafunction.html) "returning" a bool Integral Constant (http://www.mywikinet.com/mpl/ref/Integral_Constant.html), e.g. using namespace boost::mpl; template< typename T > struct silly { typedef bool_<(sizeof(T) > 50)> type; }; typedef vector< pair< silly<_1>, always<void> > , pair< always<true_>, _1 > > switch_body; typedef switch_< switch_body, char[51] >::type t1; BOOST_MPL_ASSERT_IS_SAME(t1, void); If you've got a conforming compiler, that's all. HTH, Aleksey