get rid of Attribute class. Use AttributeValue subclasses directly.

src/core/string.h

@@ -12,27 +12,10 @@ namespace ns3 {
  * This class can be used to hold variables of type string,
  * that is, either char * or std::string.
  */
-class String
-{
-public:
-  String ();
-  String (const char *value);
-  String (std::string value);
-  void Set (std::string value);
-  void Set (const char *value);
-  std::string Get (void) const;
 
-  operator std::string () const;
-
-  ATTRIBUTE_HELPER_HEADER_1 (String);
-private:
-  std::string m_value;
-};
-
-std::ostream & operator << (std::ostream &os, const String &value);
-std::istream &operator >> (std::istream &is, String &value);
-
-ATTRIBUTE_HELPER_HEADER_2 (String);
+ATTRIBUTE_VALUE_DEFINE_WITH_NAME (std::string, String);
+ATTRIBUTE_ACCESSOR_DEFINE (String);
+ATTRIBUTE_CHECKER_DEFINE (String);
 
 } // namespace ns3