chapter_07.md

Chapter 7: Object-Oriented Programming in Ruby

Overview

Object-Oriented Programming (OOP) is a programming paradigm that uses "objects" — data structures consisting of data fields and methods together with their interactions — to design applications and computer programs. Ruby is a powerful OOP language, and this chapter introduces the basic concepts of OOP in Ruby, including classes, objects, inheritance, and more.

Classes and Objects

In Ruby, classes are blueprints for creating objects (instances of classes).

Creating a Class

Here’s how to define a simple class in Ruby:

class Person
  def initialize(name)
    @name = name  # @name is an instance variable
  end

  def greet
    "Hello, #{@name}!"
  end
end

Creating Objects

You can create an object by calling the new method on a class:

alice = Person.new("Alice")
puts alice.greet  # Outputs: Hello, Alice!

Inheritance

Inheritance allows you to create a new class that is a type of an existing class.

Defining a Subclass

Here's how you can create a subclass in Ruby:

class Employee < Person
  def initialize(name, position)
    super(name)  # Calls the superclass's initialize method
    @position = position
  end

  def profile
    "#{@name} works as a #{@position}."
  end
end

Using Subclasses

bob = Employee.new("Bob", "Developer")
puts bob.profile  # Outputs: Bob works as a Developer.
puts bob.greet    # Outputs: Hello, Bob!

Encapsulation and Polymorphism

Encapsulation is the practice of keeping data (attributes) and the methods that act on the data in one object. Polymorphism is the ability of different classes to respond to the same message (method call) in different ways.

Encapsulation

You hide the object's internal state and require all interaction to be performed through object's methods.

Polymorphism Example

class Animal
  def speak
    "Some sound"
  end
end

class Dog < Animal
  def speak
    "Bark"
  end
end

class Cat < Animal
  def speak
    "Meow"
  end
end

animals = [Dog.new, Cat.new]
animals.each do |animal|
  puts animal.speak  # Outputs "Bark" for Dog and "Meow" for Cat
end