Ruby Classes and Objects

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Ruby is a pure object-oriented language where everything is an object. Classes are the blueprints for creating objects.

Defining a Class

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Use the class keyword to define a class:

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end
  
  def introduce
    puts "Hi, I'm #{@name} and I'm #{@age} years old."
  end
end

person = Person.new("Alice", 30)
person.introduce

Instance Variables

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Instance variables start with @ and belong to individual objects:

class Dog
  def initialize(name)
    @name = name
    @energy = 100
  end
  
  def bark
    puts "#{@name} says Woof!"
    @energy -= 10
  end
  
  def energy_level
    puts "Energy: #{@energy}"
  end
end

dog = Dog.new("Buddy")
dog.bark
dog.energy_level

Attribute Accessors

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Ruby provides shortcuts for getter and setter methods:

class Person
  # Creates getter and setter methods
  attr_accessor :name, :age
  
  # Only getter
  attr_reader :id
  
  # Only setter
  attr_writer :password
  
  def initialize(name, age)
    @name = name
    @age = age
    @id = rand(1000)
  end
end

person = Person.new("Bob", 25)
puts person.name  # Getter
person.age = 26   # Setter

Class Variables and Methods

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Shared across all instances of a class:

class Counter
  @@count = 0
  
  def initialize
    @@count += 1
  end
  
  def self.count
    @@count
  end
  
  def self.reset
    @@count = 0
  end
end

Counter.new
Counter.new
puts Counter.count  # 2
Counter.reset
puts Counter.count  # 0

Inheritance

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Classes can inherit from other classes:

class Animal
  def initialize(name)
    @name = name
  end
  
  def speak
    puts "#{@name} makes a sound"
  end
end

class Dog < Animal
  def speak
    puts "#{@name} barks"
  end
  
  def fetch
    puts "#{@name} fetches the ball"
  end
end

dog = Dog.new("Max")
dog.speak
dog.fetch

Super Keyword

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Call the parent class's method:

class Vehicle
  def initialize(wheels)
    @wheels = wheels
  end
  
  def info
    "This vehicle has #{@wheels} wheels"
  end
end

class Car < Vehicle
  def initialize(wheels, brand)
    super(wheels)
    @brand = brand
  end
  
  def info
    super + " and is a #{@brand}"
  end
end

car = Car.new(4, "Toyota")
puts car.info

Access Control

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Control method visibility with public, private, and protected:

class BankAccount
  def initialize(balance)
    @balance = balance
  end
  
  # Public methods (default)
  def deposit(amount)
    @balance += amount
  end
  
  def withdraw(amount)
    return unless valid_amount?(amount)
    @balance -= amount
  end
  
  def balance
    @balance
  end
  
  private
  
  # Private methods - only accessible within the class
  def valid_amount?(amount)
    amount > 0 && amount <= @balance
  end
  
  protected
  
  # Protected methods - accessible within class and subclasses
  def transfer_to(other_account, amount)
    other_account.receive(amount)
  end
  
  def receive(amount)
    @balance += amount
  end
end

Modules and Mixins

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Share functionality across classes using modules:

module Swimmable
  def swim
    puts "#{self.class} is swimming"
  end
end

module Flyable
  def fly
    puts "#{self.class} is flying"
  end
end

class Duck
  include Swimmable
  include Flyable
end

duck = Duck.new
duck.swim
duck.fly