--- a/src/common/packet.h	Wed Aug 08 09:12:55 2007 +0200
+++ b/src/common/packet.h	Wed Aug 08 09:49:56 2007 +0200
@@ -27,6 +27,7 @@
 #include "trailer.h"
 #include "tags.h"
 #include "packet-metadata.h"
+#include "tag.h"
 #include "ns3/callback.h"
 #include "ns3/assert.h"
 
@@ -470,18 +471,31 @@
 template <typename T>
 void Packet::AddTag (T const& tag)
 {
+  const Tag *parent;
+  // if the following assignment fails, it is because the
+  // input to this function is not a subclass of the Tag class.
+  parent = &tag;
   m_tags.Add (tag);
 }
 template <typename T>
 bool Packet::RemoveTag (T & tag)
 {
+  Tag *parent;
+  // if the following assignment fails, it is because the
+  // input to this function is not a subclass of the Tag class.
+  parent = &tag;
   return m_tags.Remove (tag);
 }
 template <typename T>
 bool Packet::PeekTag (T & tag) const
 {
+  Tag *parent;
+  // if the following assignment fails, it is because the
+  // input to this function is not a subclass of the Tag class.
+  parent = &tag;
   return m_tags.Peek (tag);
 }
-}; // namespace ns3
+
+} // namespace ns3
 
 #endif /* PACKET_H */

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/common/tag-registry.cc	Wed Aug 08 09:49:56 2007 +0200
@@ -0,0 +1,87 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2006 INRIA
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#include "tag-registry.h"
+#include "ns3/fatal-error.h"
+
+namespace ns3 {
+
+TagRegistry::TagInfoVector *
+TagRegistry::GetInfo (void)
+{
+  static TagRegistry::TagInfoVector vector;
+  return &vector;
+}
+
+std::string
+TagRegistry::GetUidString (uint32_t uid)
+{
+  TagInfo info = (*GetInfo ())[uid - 1];
+  return info.uidString;
+}
+uint32_t 
+TagRegistry::GetUidFromUidString (std::string uidString)
+{
+  TagInfoVector *vec = GetInfo ();
+  uint32_t uid = 1;
+  for (TagInfoVector::iterator i = vec->begin (); i != vec->end (); i++)
+    {
+      if (i->uidString == uidString)
+        {
+          return uid;
+        }
+      uid++;
+    }
+  NS_FATAL_ERROR ("We are trying to deserialize an un-registered type. This can't work.");
+  return 0;
+}
+
+void 
+TagRegistry::Destruct (uint32_t uid, uint8_t *data)
+{
+  TagInfo info = (*GetInfo ())[uid - 1];
+  info.destruct (data);
+}
+void 
+TagRegistry::Print (uint32_t uid, uint8_t *data, std::ostream &os)
+{
+  TagInfo info = (*GetInfo ())[uid - 1];
+  info.print (data, os);
+}
+uint32_t
+TagRegistry::GetSerializedSize (uint32_t uid, uint8_t *data)
+{
+  TagInfo info = (*GetInfo ())[uid - 1];
+  return info.getSerializedSize (data);
+}
+void 
+TagRegistry::Serialize (uint32_t uid, uint8_t *data, Buffer::Iterator start)
+{
+  TagInfo info = (*GetInfo ())[uid - 1];
+  info.serialize (data, start);
+}
+uint32_t 
+TagRegistry::Deserialize (uint32_t uid, uint8_t *data, Buffer::Iterator start)
+{
+  TagInfo info = (*GetInfo ())[uid - 1];
+  return info.deserialize (data, start);
+}
+
+} // namespace ns3

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/common/tag-registry.h	Wed Aug 08 09:49:56 2007 +0200
@@ -0,0 +1,149 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2006 INRIA
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#ifndef TAG_REGISTRY_H
+#define TAG_REGISTRY_H
+
+#include <string>
+#include <stdint.h>
+#include "buffer.h"
+
+namespace ns3 {
+
+/**
+ * \brief a registry of all existing tag types.
+ * \internal
+ *
+ * This class is used to give polymorphic access to the methods
+ * exported by a tag. It also is used to associate a single
+ * reliable uid to each unique type. 
+ */
+class TagRegistry
+{
+public:
+  template <typename T>
+  static uint32_t Register (std::string uidString);
+  static std::string GetUidString (uint32_t uid);
+  static uint32_t GetUidFromUidString (std::string uidString);
+  static void Destruct (uint32_t uid, uint8_t *data);
+  static void Print (uint32_t uid, uint8_t *data, std::ostream &os);
+  static uint32_t GetSerializedSize (uint32_t uid, uint8_t *data);
+  static void Serialize (uint32_t uid, uint8_t *data, Buffer::Iterator start);
+  static uint32_t Deserialize (uint32_t uid, uint8_t *data, Buffer::Iterator start);
+private:
+  typedef void (*DestructCb) (uint8_t *);
+  typedef void (*PrintCb) (uint8_t *, std::ostream &);
+  typedef uint32_t (*GetSerializedSizeCb) (uint8_t *);
+  typedef void (*SerializeCb) (uint8_t *, Buffer::Iterator);
+  typedef uint32_t (*DeserializeCb) (uint8_t *, Buffer::Iterator);
+  struct TagInfo
+  {
+    std::string uidString;
+    DestructCb destruct;
+    PrintCb print;
+    GetSerializedSizeCb getSerializedSize;
+    SerializeCb serialize;
+    DeserializeCb deserialize;
+  };
+  typedef std::vector<struct TagInfo> TagInfoVector;
+
+  template <typename T>
+  static void DoDestruct (uint8_t *data);
+  template <typename T>
+  static void DoPrint (uint8_t *data, std::ostream &os);
+  template <typename T>
+  static uint32_t DoGetSerializedSize (uint8_t *data);
+  template <typename T>
+  static void DoSerialize (uint8_t *data, Buffer::Iterator start);
+  template <typename T>
+  static uint32_t DoDeserialize (uint8_t *data, Buffer::Iterator start);
+
+  static TagInfoVector *GetInfo (void);
+};
+
+} // namespace ns3
+
+namespace ns3 {
+
+template <typename T>
+void 
+TagRegistry::DoDestruct (uint8_t *data)
+{
+  T *tag = reinterpret_cast<T *> (data);
+  tag->~T ();  
+}
+template <typename T>
+void 
+TagRegistry::DoPrint (uint8_t *data, std::ostream &os)
+{
+  T *tag = reinterpret_cast<T *> (data);
+  tag->Print (os);
+}
+template <typename T>
+uint32_t 
+TagRegistry::DoGetSerializedSize (uint8_t *data)
+{
+  T *tag = reinterpret_cast<T *> (data);
+  return tag->GetSerializedSize ();
+}
+template <typename T>
+void 
+TagRegistry::DoSerialize (uint8_t *data, Buffer::Iterator start)
+{
+  T *tag = reinterpret_cast<T *> (data);
+  tag->Serialize (start);
+}
+template <typename T>
+uint32_t 
+TagRegistry::DoDeserialize (uint8_t *data, Buffer::Iterator start)
+{
+  T *tag = reinterpret_cast<T *> (data);
+  return tag->Deserialize (start);
+}
+
+template <typename T>
+uint32_t 
+TagRegistry::Register (std::string uidString)
+{
+  TagInfoVector *vec = GetInfo ();
+  uint32_t j = 0;
+  for (TagInfoVector::iterator i = vec->begin (); i != vec->end (); i++)
+    {
+      if (i->uidString == uidString)
+        {
+          return j;
+        }
+      j++;
+    }
+  TagInfo info;
+  info.uidString = uidString;
+  info.destruct = &TagRegistry::DoDestruct<T>;
+  info.print = &TagRegistry::DoPrint<T>;
+  info.getSerializedSize = &TagRegistry::DoGetSerializedSize<T>;
+  info.serialize = &TagRegistry::DoSerialize<T>;
+  info.deserialize = &TagRegistry::DoDeserialize<T>;
+  vec->push_back (info);
+  uint32_t uid = vec->size ();
+  return uid;
+}
+
+} // namespace ns3
+
+#endif /* TAG_REGISTRY_H */

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/common/tag.h	Wed Aug 08 09:49:56 2007 +0200
@@ -0,0 +1,49 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2006 INRIA
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#ifndef TAG_H
+#define TAG_H
+
+namespace ns3 {
+
+class Tag
+{
+protected:
+  template <typename T>
+  static uint32_t AllocateUid (std::string name);
+};
+
+} // namespace ns3
+
+// implementation below.
+#include "tag-registry.h"
+
+namespace ns3 {
+
+template <typename T>
+uint32_t
+Tag::AllocateUid (std::string name)
+{
+  return TagRegistry::Register<T> (name);
+}
+
+} // namespace ns3
+
+#endif /* TAG_H */

--- a/src/common/tags.cc	Wed Aug 08 09:12:55 2007 +0200
+++ b/src/common/tags.cc	Wed Aug 08 09:49:56 2007 +0200
@@ -24,67 +24,6 @@
 
 namespace ns3 {
 
-TagRegistry::TagInfoVector *
-TagRegistry::GetInfo (void)
-{
-  static TagRegistry::TagInfoVector vector;
-  return &vector;
-}
-
-std::string
-TagRegistry::GetUidString (uint32_t uid)
-{
-  TagInfo info = (*GetInfo ())[uid - 1];
-  return info.uidString;
-}
-uint32_t 
-TagRegistry::GetUidFromUidString (std::string uidString)
-{
-  TagInfoVector *vec = GetInfo ();
-  uint32_t uid = 1;
-  for (TagInfoVector::iterator i = vec->begin (); i != vec->end (); i++)
-    {
-      if (i->uidString == uidString)
-        {
-          return uid;
-        }
-      uid++;
-    }
-  NS_FATAL_ERROR ("We are trying to deserialize an un-registered type. This can't work.");
-  return 0;
-}
-
-void 
-TagRegistry::Destruct (uint32_t uid, uint8_t data[Tags::SIZE])
-{
-  TagInfo info = (*GetInfo ())[uid - 1];
-  info.destruct (data);
-}
-void 
-TagRegistry::Print (uint32_t uid, uint8_t data[Tags::SIZE], std::ostream &os)
-{
-  TagInfo info = (*GetInfo ())[uid - 1];
-  info.print (data, os);
-}
-uint32_t
-TagRegistry::GetSerializedSize (uint32_t uid, uint8_t data[Tags::SIZE])
-{
-  TagInfo info = (*GetInfo ())[uid - 1];
-  return info.getSerializedSize (data);
-}
-void 
-TagRegistry::Serialize (uint32_t uid, uint8_t data[Tags::SIZE], Buffer::Iterator start)
-{
-  TagInfo info = (*GetInfo ())[uid - 1];
-  info.serialize (data, start);
-}
-uint32_t 
-TagRegistry::Deserialize (uint32_t uid, uint8_t data[Tags::SIZE], Buffer::Iterator start)
-{
-  TagInfo info = (*GetInfo ())[uid - 1];
-  return info.deserialize (data, start);
-}
-
 #ifdef USE_FREE_LIST
 
 struct Tags::TagData *Tags::gFree = 0;
@@ -296,10 +235,10 @@
   virtual bool RunTests (void);
 };
 
-class myTagA 
+class myTagA : public Tag
 {
 public:
-  static uint32_t GetUid (void) {static uint32_t uid = TagRegistry::Register<myTagA> ("myTagA.test.nsnam.org"); return uid;}
+  static uint32_t GetUid (void) {static uint32_t uid = AllocateUid<myTagA> ("myTagA.test.nsnam.org"); return uid;}
   void Print (std::ostream &os) const {g_a = true;}
   uint32_t GetSerializedSize (void) const {return 1;}
   void Serialize (Buffer::Iterator i) const {i.WriteU8 (a);}
@@ -307,10 +246,10 @@
 
   uint8_t a;
 };
-class myTagB 
+class myTagB : public Tag
 {
 public:
-  static uint32_t GetUid (void) {static uint32_t uid = TagRegistry::Register<myTagB> ("myTagB.test.nsnam.org"); return uid;}
+  static uint32_t GetUid (void) {static uint32_t uid = AllocateUid<myTagB> ("myTagB.test.nsnam.org"); return uid;}
   void Print (std::ostream &os) const {g_b = true;}
   uint32_t GetSerializedSize (void) const {return 4;}
   void Serialize (Buffer::Iterator i) const {i.WriteU32 (b);}
@@ -318,21 +257,21 @@
 
   uint32_t b;
 };
-class myTagC 
+class myTagC : public Tag
 {
 public:
-  static uint32_t GetUid (void) {static uint32_t uid = TagRegistry::Register<myTagC> ("myTagC.test.nsnam.org"); return uid;}
+  static uint32_t GetUid (void) {static uint32_t uid = AllocateUid<myTagC> ("myTagC.test.nsnam.org"); return uid;}
   void Print (std::ostream &os) const {g_c = true;}
   uint32_t GetSerializedSize (void) const {return Tags::SIZE;}
   void Serialize (Buffer::Iterator i) const {i.Write (c, Tags::SIZE);}
   uint32_t Deserialize (Buffer::Iterator i) {i.Read (c, Tags::SIZE); return Tags::SIZE;}
   uint8_t c [Tags::SIZE];
 };
-class myInvalidTag 
+class myInvalidTag : public Tag
 {
 public:
   static uint32_t GetUid (void) 
-  {static uint32_t uid = TagRegistry::Register<myInvalidTag> ("myinvalidTag.test.nsnam.org"); return uid;}
+  {static uint32_t uid = AllocateUid<myInvalidTag> ("myinvalidTag.test.nsnam.org"); return uid;}
   void Print (std::ostream &os) const {}
   uint32_t GetSerializedSize (void) const {return 0;}
   void Serialize (Buffer::Iterator i) const {}
@@ -340,10 +279,10 @@
 
   uint8_t invalid [Tags::SIZE+1];
 };
-class myTagZ 
+class myTagZ  : public Tag
 {
 public:
-  static uint32_t GetUid (void) {static uint32_t uid = TagRegistry::Register<myTagZ> ("myTagZ.test.nsnam.org"); return uid;}
+  static uint32_t GetUid (void) {static uint32_t uid = AllocateUid<myTagZ> ("myTagZ.test.nsnam.org"); return uid;}
   void Print (std::ostream &os) const {g_z = true;}
   uint32_t GetSerializedSize (void) const {return 0;}
   void Serialize (Buffer::Iterator i) const {}
@@ -352,11 +291,11 @@
   uint8_t z;
 };
 
-class MySmartTag 
+class MySmartTag : public Tag
 {
 public:
   static uint32_t GetUid (void) 
-  {static uint32_t uid = TagRegistry::Register<MySmartTag> ("MySmartTag.test.nsnam.org"); return uid;}
+  {static uint32_t uid = AllocateUid<MySmartTag> ("MySmartTag.test.nsnam.org"); return uid;}
   MySmartTag ()
   {
     //std::cout << "construct" << std::endl;

--- a/src/common/tags.h	Wed Aug 08 09:12:55 2007 +0200
+++ b/src/common/tags.h	Wed Aug 08 09:49:56 2007 +0200
@@ -114,128 +114,22 @@
 /**************************************************************
    An implementation of the templates defined above
  *************************************************************/
+#include "tag-registry.h"
+#include "tag.h"
 #include "ns3/assert.h"
 #include <string>
 
 namespace ns3 {
 
-/**
- * \brief a registry of all existing tag types.
- * \internal
- *
- * This class is used to give polymorphic access to the methods
- * exported by a tag. It also is used to associate a single
- * reliable uid to each unique type. 
- */
-class TagRegistry
-{
-public:
-  template <typename T>
-  static uint32_t Register (std::string uidString);
-  static std::string GetUidString (uint32_t uid);
-  static uint32_t GetUidFromUidString (std::string uidString);
-  static void Destruct (uint32_t uid, uint8_t data[Tags::SIZE]);
-  static void Print (uint32_t uid, uint8_t data[Tags::SIZE], std::ostream &os);
-  static uint32_t GetSerializedSize (uint32_t uid, uint8_t data[Tags::SIZE]);
-  static void Serialize (uint32_t uid, uint8_t data[Tags::SIZE], Buffer::Iterator start);
-  static uint32_t Deserialize (uint32_t uid, uint8_t data[Tags::SIZE], Buffer::Iterator start);
-private:
-  typedef void (*DestructCb) (uint8_t [Tags::SIZE]);
-  typedef void (*PrintCb) (uint8_t [Tags::SIZE], std::ostream &);
-  typedef uint32_t (*GetSerializedSizeCb) (uint8_t [Tags::SIZE]);
-  typedef void (*SerializeCb) (uint8_t [Tags::SIZE], Buffer::Iterator);
-  typedef uint32_t (*DeserializeCb) (uint8_t [Tags::SIZE], Buffer::Iterator);
-  struct TagInfo
-  {
-    std::string uidString;
-    DestructCb destruct;
-    PrintCb print;
-    GetSerializedSizeCb getSerializedSize;
-    SerializeCb serialize;
-    DeserializeCb deserialize;
-  };
-  typedef std::vector<struct TagInfo> TagInfoVector;
-
-  template <typename T>
-  static void DoDestruct (uint8_t data[Tags::SIZE]);
-  template <typename T>
-  static void DoPrint (uint8_t data[Tags::SIZE], std::ostream &os);
-  template <typename T>
-  static uint32_t DoGetSerializedSize (uint8_t data[Tags::SIZE]);
-  template <typename T>
-  static void DoSerialize (uint8_t data[Tags::SIZE], Buffer::Iterator start);
-  template <typename T>
-  static uint32_t DoDeserialize (uint8_t data[Tags::SIZE], Buffer::Iterator start);
-
-  static TagInfoVector *GetInfo (void);
-};
-
-template <typename T>
-void 
-TagRegistry::DoDestruct (uint8_t data[Tags::SIZE])
-{
-  T *tag = reinterpret_cast<T *> (data);
-  tag->~T ();  
-}
-template <typename T>
-void 
-TagRegistry::DoPrint (uint8_t data[Tags::SIZE], std::ostream &os)
-{
-  T *tag = reinterpret_cast<T *> (data);
-  tag->Print (os);
-}
-template <typename T>
-uint32_t 
-TagRegistry::DoGetSerializedSize (uint8_t data[Tags::SIZE])
-{
-  T *tag = reinterpret_cast<T *> (data);
-  return tag->GetSerializedSize ();
-}
-template <typename T>
-void 
-TagRegistry::DoSerialize (uint8_t data[Tags::SIZE], Buffer::Iterator start)
-{
-  T *tag = reinterpret_cast<T *> (data);
-  tag->Serialize (start);
-}
-template <typename T>
-uint32_t 
-TagRegistry::DoDeserialize (uint8_t data[Tags::SIZE], Buffer::Iterator start)
-{
-  T *tag = reinterpret_cast<T *> (data);
-  return tag->Deserialize (start);
-}
-
-template <typename T>
-uint32_t 
-TagRegistry::Register (std::string uidString)
-{
-  TagInfoVector *vec = GetInfo ();
-  uint32_t j = 0;
-  for (TagInfoVector::iterator i = vec->begin (); i != vec->end (); i++)
-    {
-      if (i->uidString == uidString)
-        {
-          return j;
-        }
-      j++;
-    }
-  TagInfo info;
-  info.uidString = uidString;
-  info.destruct = &TagRegistry::DoDestruct<T>;
-  info.print = &TagRegistry::DoPrint<T>;
-  info.getSerializedSize = &TagRegistry::DoGetSerializedSize<T>;
-  info.serialize = &TagRegistry::DoSerialize<T>;
-  info.deserialize = &TagRegistry::DoDeserialize<T>;
-  vec->push_back (info);
-  uint32_t uid = vec->size ();
-  return uid;
-}
-
 template <typename T>
 void 
 Tags::Add (T const&tag)
 {
+  const Tag *parent;
+  // if the following assignment fails, it is because the
+  // input to this function is not a subclass of the Tag class.
+  parent = &tag;
+
   NS_ASSERT (sizeof (T) <= Tags::SIZE);
   // ensure this id was not yet added
   for (struct TagData *cur = m_next; cur != 0; cur = cur->m_next) 
@@ -256,6 +150,10 @@
 bool
 Tags::Remove (T &tag)
 {
+  Tag *parent;
+  // if the following assignment fails, it is because the
+  // input to this function is not a subclass of the Tag class.
+  parent = &tag;
   NS_ASSERT (sizeof (T) <= Tags::SIZE);
   return Remove (T::GetUid ());
 }
@@ -264,6 +162,10 @@
 bool
 Tags::Peek (T &tag) const
 {
+  Tag *parent;
+  // if the following assignment fails, it is because the
+  // input to this function is not a subclass of the Tag class.
+  parent = &tag;
   NS_ASSERT (sizeof (T) <= Tags::SIZE);
   for (struct TagData *cur = m_next; cur != 0; cur = cur->m_next) 
     {

--- a/src/common/wscript	Wed Aug 08 09:12:55 2007 +0200
+++ b/src/common/wscript	Wed Aug 08 09:49:56 2007 +0200
@@ -13,6 +13,7 @@
         'packet-metadata-test.cc',
         'packet.cc',
         'tags.cc',
+        'tag-registry.cc',
         'pcap-writer.cc',
         'variable-tracer-test.cc',
         'trace-context.cc',
@@ -32,6 +33,8 @@
         'header.h',
         'trailer.h',
         'tags.h',
+        'tag-registry.h',
+        'tag.h',
         'packet.h',
         'packet-printer.h',
         'packet-metadata.h',