derived-class – Page 2

Cast base class to derived class python (or more pythonic way of extending classes)

April 4, 2023 by Tarik

If you are just adding behavior, and not depending on additional instance values, you can assign to the object’s __class__: from math import pi class Circle(object): def __init__(self, radius): self.radius = radius def area(self): return pi * self.radius**2 class CirclePlus(Circle): def diameter(self): return self.radius*2 def circumference(self): return self.radius*2*pi c = Circle(10) print c.radius print c.area() … Read more

How to define sealed class in C++?

March 26, 2023 by Tarik

C++11 solution In C++11, you can seal a class by using final keyword in the definition as: class A final //note final keyword is used after the class name { //… }; class B : public A //error – because class A is marked final (sealed). { // so A cannot be derived from. //… … Read more

Why we do create object instance from Interface instead of Class?

March 5, 2023 by Tarik

Interfaces define that a class MUST be able to do something. This means that you know the object being worked on will do what you want to be able to do. It allows you greater freedom and is one of the advantages of OOP. This is a deep topic but a very basic example would … Read more

How to dynamically create a derived type in the Python C-API

February 18, 2023 by Tarik

I encountered the same problem when I was modifying an extension to be compatible with Python 3, and found this page when I was trying to solve it. I did eventually solve it by reading the source code for the Python interpreter, PEP 0384 and the documentation for the C-API. Setting the Py_TPFLAGS_HEAPTYPE flag tells … Read more

Is it possible to assign a base class object to a derived class reference with an explicit typecast?

January 1, 2023 by Tarik

No. A reference to a derived class must actually refer to an instance of the derived class (or null). Otherwise how would you expect it to behave? For example: object o = new object(); string s = (string) o; int i = s.Length; // What can this sensibly do? If you want to be able … Read more

Why does calling a method in my derived class call the base class method?

November 19, 2022 by Tarik

There’s a difference between new and virtual/override. You can imagine, that a class, when instantiated, is nothing more than a table of pointers, pointing to the actual implementation of its methods. The following image should visualize this pretty well: Now there are different ways, a method can be defined. Each behaves different when it is … Read more