ns3: Use of pointers

In NS-3, the pointers are Ptr<T>, which is a smart pointer template that wraps a real C pointer.

Such pointer can be used as if a C pointer in most cases, such as

Ptr<obj> X, Y;
//...
X = Y;
X->function();

To assign or create a pointer, we can do either of the following:

Ptr<obj> X = CreateObject<obj>(arg1,arg2);
Ptr<obj> Y = Ptr<obj>(new obj(arg1, arg2));

The nice thing about such smart pointer is that, we can get a pointer of a derived class from a pointer of base class, just like the dynamic_cast construct in C++,

Ptr<base> X;
//...
Ptr<derived> Y = X->GetObject<derived>();
Ptr<derived> Z = DynamicCast<derived>(X);

The GetObject is preferred because in NS-3, we have object aggregation as well as object hierarchy. The DynamicCast construct works only for the object hierarchy but GetObject works for both.