observer.rb

# Your code here!
class Notify
  def exec(*data)
    raise NotImplementedError.new("#{self.class}##{__method__} が実装されていません")
  end
end

class User< Notify
  def exec(*data)
    puts "send to User #{data}"
  end
end

class AdminUser < Notify
  def exec(*data)
    puts "send to AdminUser #{data}"
  end
end


class Subscribe
  def initialize
    @subscribers = []
  end
  
  def set(ins)
    @subscribers.push(ins)
    self
  end

  def exec(*data)
    @subscribers.each { |ins| ins.exec(*data) }
  end
end


sub = Subscribe.new()
sub.set(User.new).set(AdminUser.new).set(User.new).set(AdminUser.new).set(User.new)
sub.exec("🌵", "🐎")