Index: shared_array.hpp
===================================================================
--- shared_array.hpp	(revision 52581)
+++ shared_array.hpp	(working copy)
@@ -35,6 +35,40 @@
 namespace boost
 {
 
+namespace detail
+{
+  template <class T> struct sa_wrap {};
+
+  //is T a const-qualified version of Y?
+  template< class T, class Y > struct is_const_version_impl
+  {
+    typedef char (&yes) [1];
+    typedef char (&no)  [2];
+
+    static yes f( const sa_wrap<Y const>& );
+    static no  f( ... );
+
+    enum _vt { value = sizeof( f( sa_wrap<T>() ) ) == sizeof(yes) };
+  };
+
+  struct sa_empty {};
+
+  template <bool> struct sa_is_const;
+
+  template <> struct sa_is_const<true>
+  {
+    typedef sa_empty type;
+  };
+
+  template <> struct sa_is_const<false>
+  {};
+
+  template <class T, class Y>
+  struct sa_enable
+    : public sa_is_const<is_const_version_impl<T, Y>::value>
+  {};
+}
+
 //
 //  shared_array
 //
@@ -69,8 +103,15 @@
     {
     }
 
-//  generated copy constructor, assignment, destructor are fine
+//  generated assignment, destructor are fine
 
+    template <class Y>
+    shared_array(shared_array<Y> const & other,
+        typename detail::sa_enable<T, Y>::type = detail::sa_empty()) // never throws
+      : px(other.px),
+        pn(other.pn)
+    {}
+
     void reset(T * p = 0)
     {
         BOOST_ASSERT(p == 0 || p != px);
@@ -115,6 +156,8 @@
 
 private:
 
+    template <class Y> friend class shared_array;
+
     T * px;                     // contained pointer
     detail::shared_count pn;    // reference counter