Introduction to Polymorphism in Ruby

Welcome back! We're continuing our journey into object-oriented programming (OOP) with a new and exciting topic: Polymorphism. You've already learned about classes, objects, and inheritance, which are essential building blocks of OOP. Now, it's time to explore how polymorphism can make your code more flexible and reusable.

Polymorphism allows objects to be treated as instances of their parent class rather than their actual class. This provides a way to use a single interface to represent different types of objects. Here’s what we’ll cover in this lesson:

1. Understanding Polymorphism: We'll discuss what polymorphism is and why it's a powerful concept in Ruby programming.
2. Implementing Polymorphism in Ruby: You'll learn how to use method overriding and duck typing to achieve polymorphism.

Polymorphism in Ruby allows you to call methods of derived classes through a base class reference. This makes your code more dynamic and general. For example, consider the following Ruby code:

# Define a base class Person with name and age attributes
class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  # Define a display method, which can be overridden by derived classes
  def display
    puts "Name: #{@name}, Age: #{@age}"
  end
end

# Define a derived class Student with a major attribute
class Student < Person
  def initialize(name, age, major)
    super(name, age)
    @major = major
  end

  # Override the display method to include the major attribute
  def display
    super
    puts "Major: #{@major}"
  end
end

# Define a derived class Teacher with a subject attribute
class Teacher < Person
  def initialize(name, age, subject)
    super(name, age)
    @subject = subject
  end

  # Override the display method to include the subject attribute
  def display
    super
    puts "Subject: #{@subject}"
  end
end

# Creating instances of Student and Teacher
person1 = Student.new("Alice", 30, "Computer Science")
person2 = Teacher.new("Bob", 25, "Mathematics")

# Calling the display method on both instances
person1.display
person2.display

In this example, the display method of the derived classes (Student and Teacher) overrides the base class method in Person. When we call display on an instance of Student or Teacher, the Ruby interpreter automatically invokes the appropriate derived class method.

Let's also understand how Ruby resolves methods. Ruby uses a method lookup chain to resolve which method to invoke. When person1.display is called, Ruby first checks if the display method exists in the Student class. If found, it executes it. If not, it moves up to the Person class.