concern_with_all.rb

require "active_support/concern"

module M
  extend ActiveSupport::Concern

  included do
    has_many :things
    scope :disabled, -> { where(disabled: true) }
    after_commit :send_email
    validates :email, length: { maximum: 255 }, email: true
  end

  def instance_method
  end

  class_methods do
    ...
  end
  
  private
  
  def send_email
    send_emails_here
  end
end