[Boost-users] MPL if_ not following true branch

Subject: [Boost-users] MPL if_ not following true branch
From: Cory Nelson (phrosty_at_[hidden])
Date: 2009-05-18 03:33:10

This code doesn't seem to ever follow the true branch of the if_...
it's like the eval_if is clobbering it.  Can someone tell me what I'm
doing wrong (other than not using a map.. this is a reduction of some
other code that can't use a map)?

#include <iostream>
#include <typeinfo>
#include <boost/mpl/if.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/static_assert.hpp>

template<typename T>
struct choose_type
{
        struct int_tag {};
        struct float_tag {};

        template<typename InvalidT>
        struct invalid_type_specified
        {
                BOOST_STATIC_ASSERT(sizeof(InvalidT) == 0);
        };

        typedef typename boost::mpl::if_<
                boost::is_same<T, int>,
                int_tag,
                typename boost::mpl::eval_if<
                        boost::is_same<T, float>,
                        boost::mpl::identity<float_tag>,
                        invalid_type_specified<T>
		>::type
	>::type type;
};

int main()
{
        std::cout << typeid(choose_type<int>::type).name() << std::endl;
        return 0;
}

-- 
Cory Nelson