Simple Publisher

ClassUsingPublisher.rb

require 'publisher'

class CreateGroupEmail
  include Publisher

  def initialize(payload)
    @payload = payload
  end

  def call
    return unless group_user
    users = build_group(Group.create(user_id: group_user.id,
                                     groupname: payload_subject))

    publish { |listener| listener.new_group(payload, users.map(&:strip)) }
  end

DefinitionOfUse.rb

  # Could be a method in any class, the class wouldn't have to include the publisher
  def create_group
    @create_group ||= CreateGroupEmail.new(payload).tap do |publisher|
      publisher.add_consumer(InformUser.new)
    end
  end

InformUser.rb

class InformUser
  def add_member(payload)
    AddMemberMailer.notification(payload).deliver
  end

  def remove_member(payload)
    RemoveMemberMailer.notification(payload).deliver
  end

  def help_user(payload)
    HelpUserMailer.notification(payload).deliver
  end

  def new_group(payload, users)
    NewGroupMailer.notification(payload, users).deliver
  end
end

publisher.rb

require 'set'

module Publisher
  def publish(&block)
    consumers.each(&block)
  end

  def add_consumer(listener)
    consumers.add(listener)
  end

  def consumers
    @consumers ||= Set.new
  end
end