The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...

3.5 Class TclClassThis compiled class (class TclClass) is a pure virtual class. Classes derived from this base class provide two functions:construct the interpreted class hierarchy to mirror the compiled class hierarchy; and provide methods to instantiate newTclObjects. Each such derived class is associated with a particular compiled class in the compiled class hierarchy, and caninstantiate new objects in the associated class.As an example, consider a class such as the class RenoTcpClass. It is derived from class TclClass, and is associatedwith the class RenoTcpAgent. It will instantiate new objects in the class RenoTcpAgent. The compiled class hierarchyfor RenoTcpAgent is that it derives from TcpAgent, that in turn derives from Agent, that in turn derives (roughly) fromTclObject. RenoTcpClass is defined asstatic class RenoTcpClass: public TclClass {public:RenoTcpClass() : TclClass("Agent/TCP/Reno") {}TclObject* create(int argc, const char*const* argv) {return (new RenoTcpAgent());}} class_reno;We can make the following observations from this definition:1. The class defines only the constructor, and one additional method, to create instances of the associated TclObject.2. ns will execute the RenoTcpClass constructor for the static variable class_reno, when it is first started. This setsup the appropriate methods and the interpreted class hierarchy.3. The constructor specifies the interpreted class explicitly as Agent/TCP/Reno. This also specifies the interpretedclass hierarchy implicitly.Recall that the convention in ns is to use the character slash (’/’) is a separator. For any given class A/B/C/D, theclass A/B/C/D is a sub-class of A/B/C, that is itself a sub-class of A/B, that, in turn, is a sub-class of A. A itself is asub-class of TclObject.In our case above, the TclClass constructor creates three classes, Agent/TCP/Reno sub-class of Agent/TCP subclassof Agent sub-class of TclObject.4. This class is associated with the class RenoTcpAgent; it creats new objects in this associated class.5. The RenoTcpClass::create method returns TclObjects in the class RenoTcpAgent.6. When the user specifies new Agent/TCP/Reno, the routine RenoTcpClass::create is invoked.7. The arguments vector (argv) consists of— argv[0] contains the name of the object.— argv[1...3] contain $self, $class, and $proc.Since create is called through the instance procedurecreate-shadow, argv[3] contains create-shadow.— argv[4] contain any additional arguments (passed as a string) provided by the user.The class Trace illustrates argument handling by TclClass methods.class TraceClass : public TclClass {public:30