Classes

Classes in Ruby

A class is a blueprint for objects. Define one with class and end:

class Dog
  def initialize(name)
    @name = name    # instance variable
  end

  def bark
    "#{@name} says: Woof!"
  end
end

dog = Dog.new("Rex")
puts dog.bark    # Rex says: Woof!

Instance Variables

Instance variables start with @ and are private by default. Use attr_reader, attr_writer, or attr_accessor to expose them:

class Person
  attr_reader :name     # creates a getter
  attr_accessor :age    # creates getter and setter

  def initialize(name, age)
    @name = name
    @age = age
  end
end

p = Person.new("Alice", 30)
puts p.name   # Alice
p.age = 31
puts p.age    # 31

to_s

Override to_s to control how an object is printed:

class Point
  def initialize(x, y)
    @x = x
    @y = y
  end

  def to_s
    "(#{@x}, #{@y})"
  end
end

puts Point.new(3, 4)  # (3, 4)

Scope Resolution Operator (::)

The :: operator accesses constants and methods inside a module or class. For example, Math::PI retrieves the PI constant from the built-in Math module. You'll see this pattern frequently with namespaced code.

Your Task

Create a Circle class with:

• initialize(radius) — stores the radius as @radius
• area — returns (Math::PI * @radius ** 2).round(2)
• to_s — returns "Circle(radius=<radius>)"

Create Circle.new(5), print its string form and its area.