Ruby Classes and Objects #

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

Defining a Class #

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 #

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 #

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 #

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 #

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 #

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 #

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 #

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