added is_reference_wrapper<>, unwrap_reference<>

[SVN r12470]

include/boost/ref.hpp

@@ -25,6 +25,7 @@ namespace boost
 template<class T> class reference_wrapper
 { 
 public:
+    typedef T type;
 
     explicit reference_wrapper(T & t): t_(t) {}
 
@@ -57,6 +58,86 @@ template<class T> inline reference_wrapper<T const> BOOST_REF_CONST cref(T const
 
 # undef BOOST_REF_CONST
 
+# ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+template<typename T>
+class is_reference_wrapper
+{
+ public:
+    BOOST_STATIC_CONSTANT(bool, value = false); 
+};
+
+template<typename T>
+class is_reference_wrapper<reference_wrapper<T> >
+{
+ public:
+    BOOST_STATIC_CONSTANT(bool, value = true);
+};
+
+template<typename T>
+class unwrap_reference
+{
+ public:
+    typedef T type;
+};
+
+template<typename T>
+class unwrap_reference<reference_wrapper<T> >
+{
+ public:
+    typedef T type;
+};
+# else // no partial specialization
+namespace detail
+{
+  typedef char (&yes_reference_wrapper_t)[1];
+  typedef char (&no_reference_wrapper_t)[2];
+      
+  no_reference_wrapper_t is_reference_wrapper_test(...);
+
+  template<typename T>
+  yes_reference_wrapper_t is_reference_wrapper_test(reference_wrapper<T>*);
+
+  template<bool wrapped>
+  struct reference_unwrapper
+  {
+      template <class T>
+      struct apply
+      {
+          typedef T type;
+      };
+  };
+
+  template<>
+  struct reference_unwrapper<true>
+  {
+      template <class T>
+      struct apply
+      {
+          typedef typename T::type type;
+      };
+  };
+}
+
+template<typename T>
+class is_reference_wrapper
+{
+ public:
+    static T* t;
+    BOOST_STATIC_CONSTANT(
+        bool, value = (
+            sizeof(detail::is_reference_wrapper_test(t))
+            == sizeof(detail::yes_reference_wrapper_t)));
+};
+
+template <typename T>
+class unwrap_reference
+    : public detail::reference_unwrapper<
+        is_reference_wrapper<T>::value
+      >::template apply<T>
+{};
+
+# endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+
 } // namespace boost
 
 #endif // #ifndef BOOST_REF_HPP_INCLUDED