example of usage of concerns

phone_number.rb

# app/models/concerns/phone_number.rb
# concern to validate spanish phone numbers and provide some custom formatters
module PhoneNumber
  extend ActiveSupport::Concern

  PHONE_REGEXP = /\+\d{2}\s\d{3}\s\d{3}\s\d{3}/.freeze # e.g. +34 900 123 123
  
  included do
    validates :phone_number, presence: true, format: { with: PHONE_REGEXP, message: "invalid phone number" }
  end
  
  def phone_format_00
    phone_number.gsub(/\+/, '00')
  end
end

store.rb

# app/models/store.rb
class Store < ActiveRecord::Base
  include PhoneNumber
end

user.rb

# app/models/user.rb
class User < ActiveRecord::Base
  include PhoneNumber
end