exclude-example.rb

module Miouable
  def miouw
    puts 'miouw !'
  end
end

class CatWithExtend
  extend Miouable
end

cat = CatWithExtend.new
cat.miouw 
# NoMethodError
# undefined method miouw

CatWithExtend.miouw
# miouw !

include-example.rb

module Miouable
  def miouw
    puts 'miouw !'
  end
end

class Cat 
  include Miouable 
end

cat = Cat.new 
cat.miouw 
# miouw !

Cat.miouw 
# NoMethodError
# undefined method miouw for Cat:Class

pokemon-after-scope.rb

class Pokemon < ApplicationRecord

  scope :active, where(active: true)
  scope :red, where(color: 'red')
  scope :with_evolution, where.not(next_evolution: nil)
  scope :not_savage, where.not(owner_id: 0)

  scope :lvl, -> (level) { where(level: level) }

  def self.all_active_red_with_evolution_and_not_savage
    active.red.with_evolution.not_savage
  end

  def self.all_red_with_evolution
    red.with_evolution
  end

  def all_red_with_evolution_at_level_max
    red.with_evolution.lvl(100)
  end

end

pokemon-before-scope.rb

class Pokemon < ApplicationRecord

  def self.all_active_red_with_evolution_and_not_savage
    where(active: true).where(color: 'red').where.not(next_evolution: nil).where.not(owner_id: 0)
  end

end