From 43a9571b2c9f7364e3bd644eb30b8d35f63cacbc Mon Sep 17 00:00:00 2001
From: Dave Abrahams <dave@boostpro.com>
Date: Fri, 29 Nov 2002 22:43:27 +0000
Subject: [PATCH] Fixed some technical problems with smart pointer support
 uncovered by STLPort's debug mode. Unfortunately, had to expand
 Dereferenceable requirements.

[SVN r16459]
---
 doc/v2/Dereferenceable.html                   | 17 +++++++++++++-
 .../boost/python/object/pointer_holder.hpp    | 22 +++++++++++++++++--
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/doc/v2/Dereferenceable.html b/doc/v2/Dereferenceable.html
index 8f5b38b5..965e4043 100644
--- a/doc/v2/Dereferenceable.html
+++ b/doc/v2/Dereferenceable.html
@@ -49,10 +49,25 @@ type is a model of Dereferenceable.
   </tr>
 </table>
 
+If <code><b>x</b></code> is not a pointer type, it also must satsify the following expression:
+
+<table summary="Dereferenceable expressions" border="1" cellpadding="5">
+
+  <tr> 
+    <td><b>Expression</b></td>
+    <td><b>Operational Semantics</b></td>
+  </tr>
+
+  <tr> 
+    <td valign="top"><code>x.get()</code></td>
+    <td><code>&amp;*x</code>, or a null pointer
+  </tr>
+</table>
+
 <hr>
 <p>Revised 
   <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
-  13 November, 2002
+  29 November, 2002
   <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
 </p>
     <p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
diff --git a/include/boost/python/object/pointer_holder.hpp b/include/boost/python/object/pointer_holder.hpp
index 3a65dcb3..5625f092 100644
--- a/include/boost/python/object/pointer_holder.hpp
+++ b/include/boost/python/object/pointer_holder.hpp
@@ -32,6 +32,18 @@
 
 namespace boost { namespace python { namespace objects {
 
+template <class T>
+typename bool is_null(T const& p, ...)
+{
+    return p.get() == 0;
+}
+
+template <class T>
+bool is_null(T* p, int)
+{
+    return p == 0;
+}
+
 #  define BOOST_PYTHON_UNFORWARD_LOCAL(z, n, _) BOOST_PP_COMMA_IF(n) (typename unforward<A##n>::type)(a##n)
 
 template <class Pointer, class Value>
@@ -98,9 +110,12 @@ void* pointer_holder<Pointer, Value>::holds(type_info dst_t)
     if (dst_t == python::type_id<Pointer>())
         return &this->m_p;
 
+    if (objects::is_null(this->m_p, 0))
+        return 0;
+    
     type_info src_t = python::type_id<Value>();
-    return src_t == dst_t ? &*this->m_p
-        : find_dynamic_type(&*this->m_p, src_t, dst_t);
+    Value* p = &*this->m_p;
+    return src_t == dst_t ? p : find_dynamic_type(p, src_t, dst_t);
 }
 
 template <class Pointer, class Value>
@@ -109,6 +124,9 @@ void* pointer_holder_back_reference<Pointer, Value>::holds(type_info dst_t)
     if (dst_t == python::type_id<Pointer>())
         return &this->m_p;
 
+    if (objects::is_null(this->m_p, 0))
+        return 0;
+    
     if (dst_t == python::type_id<held_type>())
         return &*this->m_p;