OOP is a programming paradigm based on the concept of “objects”, which may contain data, in the form of fields often known as attributes; and code in the form of procedures, often known as methods. We are aiming to group related data and functions.
- Encapsulation: tie the data and the functions that are acting together in a class.
- Composition
- Delegation is calling a routine “in another context”, for instance calling a base class member function from an instance of a derived class.
- Open recursion
- Abstraction: providing only essential information to the outside world and hiding their background details, separation of interface and implementation.
- Decoupling: removing dependencies on external computations/data.
- Low coupling, high cohesion
Virtual tables
A non-virtual class has a size of 1 because in C++ classes can’t have zero size.
A virtual class has a size of 8 on a 64 bit machine because there’s a hidden pointer inside it pointing to a vtable. vtables are static translation tables, created for each virtual-class.
#include <iostream>
int main() {
struct A {
} a;
struct B {
virtual void func(){;}
} b;
std::cout << (sizeof a) << "\n";
std::cout << (sizeof b) << "\n";
}
Polymorphism
Polymorphism means “many forms” and describes the ability of an operation to change behaviour according to its arguments.
Ad-hoc polymorphism
Function and operator overloading.
Writeln(Add(1, 2)); (* Prints "3" *)
Writeln(Add('Hello, ', 'World!')); (* Prints "Hello, World!" *)
Parametric polymorphism
Function does the same thing for different types: templates in C++.
Sub-typing (inheritance)
Class hierarchies, diamond inheritance.
Static and dynamic polymorphism
Polymorphism can be distinguished by when the implementation is selected: statically (at compile time) or dynamically (at run time, typically via a virtual function). This is known respectively as static dispatch and dynamic dispatch, and the corresponding forms of polymorphism are accordingly called static polymorphism and dynamic polymorphism.
- Stack overflow
- Polymorphism
- What’s the difference between malloc and new?
- Compare functional and object-oriented programming