Re: Re: mpl::if_ or mpl::apply_if?

From: Markus Werle (yg-boost-users_at_[hidden])
Date: 2003-02-26 08:13:18

Aleksey Gurtovoy wrote:

 
> With the current CVS, you don't have to do it by yourself:
> 
> #include "boost/mpl/vector.hpp"
> #include "boost/mpl/switch.hpp"
> #include "boost/mpl/project1st.hpp"
> #include "boost/mpl/pair.hpp"
> #include "boost/mpl/always.hpp"
> #include "boost/mpl/bool_c.hpp"
> #include "boost/mpl/assert_is_same.hpp"
> 
> #include "boost/type_traits/remove_reference.hpp"
> #include "boost/type_traits/add_const.hpp"
> #include "boost/type_traits/is_pointer.hpp"
> #include "boost/type_traits/is_reference.hpp"
> 
> 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);
> 
> Does it cover your needs?

It covers my needs and it makes me feel like a stupid 
KnowNothing (after 5 years in expression template 
metaprogramming)

What are the requirements for the struct 
some_condition<_1> to be used in such a switch body?

Markus