[boost] [PATCH]Enhancing any_cast

From: Mikhail Glushenkov (bbman_at_[hidden])
Date: 2004-12-10 16:15:09

This is an enhanced version of Unai Uribarri's 
patch  (see 
http://lists.boost.org/MailArchives/boost/msg42284.php 
).
Adds support for the following syntax:

boost::any a = 7;
int& i = any_cast<int&>(a);

Current syntax for reference extraction is

int& i = *any_cast<int>(&a);

Old syntax is preserved.
On compilers without support for partial 
template specialization users are required to 
provide explicit specializations of 
boost::remove_reference for their classes 
(usually via 
BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION) 
if they want to use the new syntax.
Patch was tested on msvc 6 and 7.1, intel 8.1 
and gcc 3.3.1.
If this patch will be accepted, I'll write 
tests/update documentation.


--- any.hpp Thu Sep 16 11:23:30 2004
+++ new_any.hpp Fri Dec 10 19:47:45 2004
@@ -15,6 +15,12 @@
 
 #include "boost/config.hpp"
 #include <boost/throw_exception.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+
+#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+#include <boost/type_traits/is_reference.hpp>
+#include <boost/static_assert.hpp>
+#endif
 
 namespace boost
 {
@@ -168,12 +174,39 @@
     }
 
     template<typename ValueType>
-    ValueType any_cast(const any & operand)
+    const ValueType any_cast(const any & operand)
     {
-        const ValueType * result = any_cast<ValueType>(&operand);
+    #ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+        // Please use BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION macro
+        // to generate specialization of remove_reference for your class
+        // See type traits library documentation for details
+        BOOST_STATIC_ASSERT(!::boost::is_reference< 
+            boost::remove_reference<ValueType>::type >::value);
+   
+    #endif //BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+       
+        typedef typename boost::remove_reference<ValueType>::type Type;
+        const Type * result = any_cast<Type>(&operand);
         if(!result)
             boost::throw_exception(bad_any_cast());
         return *result;
+    }
+
+    template<typename ValueType>
+    ValueType any_cast(any & operand)
+    {
+    #ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+        // Please use BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION macro
+        // to generate specialization of remove_reference for your class
+        // See type traits library documentation for details
+        BOOST_STATIC_ASSERT(!::boost::is_reference< 
+            boost::remove_reference<ValueType>::type >::value);
+
+    #endif //BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+       
+        typedef typename boost::remove_reference<ValueType>::type Type; 
+        Type * result = any_cast<Type>(&operand);
+        if(!result)
+            boost::throw_exception(bad_any_cast());
+        return *result;
     }
 
 }