--- a/src/common/tags.cc	Thu Feb 01 18:50:19 2007 +0100
+++ b/src/common/tags.cc	Thu Feb 01 18:50:58 2007 +0100
@@ -42,7 +42,7 @@
   	m_sorted = true;
     }
   assert (m_sorted);
-  uint32_t uid = 0;
+  uint32_t uid = 1;
   for (TagsDataCI i = m_registry.begin (); i != m_registry.end (); i++) 
     {
   	if (i->first == uuid) 
@@ -52,8 +52,7 @@
   	uid++;
     }
   // someone asked for a uid for an unregistered uuid.
-  assert ("You tried to use unregistered tag: make sure you create an "
-  		"instance of type TagRegistration<YouTagType>.");
+  assert (!"You tried to use unregistered tag: make sure you create an instance of type TagRegistration<YouTagType>.");
   // quiet compiler
   return 0;
 }
@@ -101,6 +100,7 @@
     }
   gN_free++;
   data->m_next = gFree;
+  data->m_id = 0;
   gFree = data;
 }
 #else
@@ -203,17 +203,17 @@
 };
 
 static void 
-myTagAPrettyPrinterCb (struct myTagA *a, std::ostream &os)
+myTagAPrettyPrinterCb (struct myTagA const*a, std::ostream &os)
 {
   os << "struct myTagA, a="<<(uint32_t)a->a<<std::endl;
 }
 static void 
-myTagBPrettyPrinterCb (struct myTagB *b, std::ostream &os)
+myTagBPrettyPrinterCb (struct myTagB const*b, std::ostream &os)
 {
   os << "struct myTagB, b="<<b->b<<std::endl;
 }
 static void 
-myTagCPrettyPrinterCb (struct myTagC *c, std::ostream &os)
+myTagCPrettyPrinterCb (struct myTagC const*c, std::ostream &os)
 {
   os << "struct myTagC, c="<<(uint32_t)c->c[0]<<std::endl;
 }

--- a/src/common/tags.h	Thu Feb 01 18:50:19 2007 +0100
+++ b/src/common/tags.h	Thu Feb 01 18:50:58 2007 +0100
@@ -96,10 +96,10 @@
    * \param fn a function which can pretty-print an instance
    *        of type T in the output stream.
    */
-  TagRegistration<T> (std::string uuid, void(*fn) (T *, std::ostream &));
+  TagRegistration<T> (std::string uuid, void(*fn) (T const*, std::ostream &));
 private:
   static void PrettyPrinterCb (uint8_t *buf, std::ostream &os);
-  static void(*m_prettyPrinter) (T *, std::ostream &);
+  static void(*m_prettyPrinter) (T const*, std::ostream &);
 };
 
 }; // namespace ns3
@@ -118,6 +118,10 @@
 public:
   typedef void (*PrettyPrinter) (uint8_t [Tags::SIZE], std::ostream &);
   static void Record (std::string uuid, PrettyPrinter prettyPrinter);
+  /**
+   * returns a numeric integer which uniquely identifies the input string.
+   * that integer cannot be zero which is a reserved value.
+   */
   static uint32_t LookupUid (std::string uuid);
   static void PrettyPrint (uint32_t uid, uint8_t buf[Tags::SIZE], std::ostream &os);
 private:
@@ -173,7 +177,7 @@
  * the call to the user-provided function.
  */
 template <typename T>
-TagRegistration<T>::TagRegistration (std::string uuid, void (*prettyPrinter) (T *, std::ostream &))
+TagRegistration<T>::TagRegistration (std::string uuid, void (*prettyPrinter) (T const*, std::ostream &))
 {
   assert (sizeof (T) <= Tags::SIZE);
   m_prettyPrinter  = prettyPrinter;
@@ -190,7 +194,7 @@
 }
 
 template <typename T>
-void (*TagRegistration<T>::m_prettyPrinter) (T *, std::ostream &) = 0;
+void (*TagRegistration<T>::m_prettyPrinter) (T const*, std::ostream &) = 0;