abstract class

[toraj58]

pure virtual function declaration provide the prototype of the method. but an implementation of the pure virtual function is typically not provided in an abstract class (in 99% of situations), but it may be included. Every non-abstract child class is still required to override the method, but the implementation provided by the abstract class may be called in this way:

class Abstract {
public:
   virtual void pure_virtual() = 0;
 };

 void Abstract::pure_virtual() {
   // do something
 }
 
 class Child : public Abstract {
   virtual void pure_virtual(); // no longer abstract, this class may be
                                // instantiated.
 };
 
 void Child::pure_virtual() {
   Abstract::pure_virtual(); // the implementation in the abstract class 
                             // is executed
 }

this is the flexibility of C++ but i am not sure we can do such thing in C#!