Constexpr conversion to MPL types

Author: Kojoley

include/boost/type_traits/integral_constant.hpp

@@ -57,12 +57,8 @@ namespace boost{
       typedef integral_constant<T, val> type;
       static const T value = val;
 
-      operator const mpl::integral_c<T, val>& ()const
-      {
-         static const char data[sizeof(long)] = { 0 };
-         static const void* pdata = data;
-         return *(reinterpret_cast<const mpl::integral_c<T, val>*>(pdata));
-      }
+      BOOST_CONSTEXPR operator mpl::integral_c<T, val>()const
+      { return mpl::integral_c<T, val>(); }
       BOOST_CONSTEXPR operator T()const { return val; }
    };
 
@@ -77,12 +73,8 @@ namespace boost{
       typedef integral_constant<bool, val> type;
       static const bool value = val;
 
-      operator const mpl::bool_<val>& ()const
-      {
-         static const char data[sizeof(long)] = { 0 };
-         static const void* pdata = data;
-         return *(reinterpret_cast<const mpl::bool_<val>*>(pdata));
-      }
+      BOOST_CONSTEXPR operator mpl::bool_<val>()const
+      { return mpl::bool_<val>(); }
       BOOST_CONSTEXPR operator bool()const { return val; }
    };
 

test/mpl_interop_test1.cpp

@@ -5,26 +5,41 @@
 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
 #include <boost/type_traits/is_void.hpp>
+#include <boost/mpl/bool.hpp>
+#include <boost/config.hpp>
 
 template <class T>
-int dispatch_test_imp(const boost::mpl::bool_<true>&)
+BOOST_CONSTEXPR int dispatch_test_imp1(const boost::mpl::bool_<true>&)
 {
    return 0;
 }
 template <class T>
-int dispatch_test_imp(const boost::mpl::bool_<false>&)
+BOOST_CONSTEXPR int dispatch_test_imp1(const boost::mpl::bool_<false>&)
 {
    return 1;
 }
 
 template <class T>
-int dispatch_test()
+BOOST_CONSTEXPR int dispatch_test_imp2(boost::mpl::true_)
 {
-   return dispatch_test_imp<T>(boost::is_void<T>());
+   return 0;
+}
+template <class T>
+BOOST_CONSTEXPR int dispatch_test_imp2(boost::mpl::false_)
+{
+   return 1;
+}
+
+template <class T>
+BOOST_CONSTEXPR int dispatch_test()
+{
+   return dispatch_test_imp1<T>(boost::is_void<T>()) +
+          dispatch_test_imp2<T>(boost::is_void<T>());
 }
 
 
 int main()
 {
-   return (dispatch_test<int>() == 1) && (dispatch_test<void>() == 0) ? 0 : 1;
+   BOOST_CONSTEXPR bool result = (dispatch_test<int>() == 2) && (dispatch_test<void>() == 0);
+   return result ? 0 : 1;
 }