class Person
   # extend and include go first
   extend SomeModule
   include AnotherModule

   # constants are next
   SOME_CONSTANT = 20

   # afterwards we have attribute macros
   attr_reader :name

   # followed by other macros (if any)
   validates :name

   # public class methods are next in line
   def self.some_method
   end

   # followed by public instance methods
   def some_method
   end

   # protected and private methods are grouped near the end
   protected

   def some_protected_method
   end

   private

   def some_private_method
   end
  end

 # bad
  class SomeClass
   def self.some_method
    # body omitted
   end

   def self.some_other_method
   end
  end

  # good
  module SomeClass
   module_function

   def some_method
    # body omitted
   end

   def some_other_method
   end
  end

  # bad
  module Utilities
   extend self

   def parse_something(string)
    # do stuff here
   end

   def other_utility_method(number, string)
    # do some more stuff
   end
  end

  # good
  module Utilities
   module_function

   def parse_something(string)
    # do stuff here
   end

   def other_utility_method(number, string)
    # do some more stuff
   end
  end

 class Person
   attr_reader :first_name, :last_name

   def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
   end

   def to_s
    "#@first_name #@last_name"
   end
  end

 # bad
  class Person
   def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
   end

   def first_name
    @first_name
   end

   def last_name
    @last_name
   end
  end

  # good
  class Person
   attr_reader :first_name, :last_name

   def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
   end
  end

  # bad - creates a single attribute accessor (deprecated in 1.9)
  attr :something, true
  attr :one, :two, :three # behaves as attr_reader

  # good
  attr_accessor :something
  attr_reader :one, :two, :three

  # good
  class Person
   attr_reader :first_name, :last_name

   def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
   end
  end

  # better
  class Person < Struct.new(:first_name, :last_name)
  end

  # good
  class Person
   attr_accessor :first_name, :last_name

   def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
   end
  end

  # better
  Person = Struct.new(:first_name, :last_name) do
  end

class Person
   def self.create(potions_hash)
    # body omitted
   end
  end

 # bad
  class Animal
   # abstract method
   def speak
   end
  end

  # extend superclass
  class Duck < Animal
   def speak
    puts 'Quack! Quack'
   end
  end

  # extend superclass
  class Dog < Animal
   def speak
    puts 'Bau! Bau!'
   end
  end

  # good
  class Duck
   def speak
    puts 'Quack! Quack'
   end
  end

  class Dog
   def speak
    puts 'Bau! Bau!'
   end
  end

 class Parent
   @@class_var = 'parent'

   def self.print_class_var
    puts @@class_var
   end
  end

  class Child < Parent
   @@class_var = 'child'
  end

  Parent.print_class_var # => will print "child"

 class SomeClass
   def public_method
    # ...
   end

   private

   def private_method
    # ...
   end

   def another_private_method
    # ...
   end
  end

  class TestClass
   # bad
   def TestClass.some_method
    # body omitted
   end

   # good
   def self.some_other_method
    # body omitted
   end

   # Also possible and convenient when you
   # have to define many singleton methods.
   class << self
    def first_method
     # body omitted
    end

    def second_method_etc
     # body omitted
    end
   end
  end

  class SingletonTest
   def size
    25
   end
  end

  test1 = SingletonTest.new
  test2 = SingletonTest.new
  def test2.size
   10
  end
  test1.size # => 25
  test2.size # => 10