Demeter

The Law of Demeter (LoD), or Principle of Least Knowledge, is a simple design style for developing software with the following guidelines:

• Each unit should have only limited knowledge about other units: only units "closely" related to the current unit.
• Each unit should only talk to its friends; don't talk to strangers.
• Only talk to your immediate friends.

Installation

sudo gem install demeter

Usage

require "demeter"

class User
  extend Demeter

  demeter :address

  attr_accessor :name
  attr_accessor :address

  def initialize
    @address = Address.new
  end
end

class Address
  attr_accessor :country
end

user = User.new
user.address.country = "Brazil"
user.address_country
#=> Brazil

If your using ActiveRecord, you don't have to extend the Demeter module.

class User < ActiveRecord::Base
  has_one :address
  demeter :address
end

user = User.first
user.address_country

You can easily override a method that has been "demeterized"; just declare it before or after calling the demeter method.

class User < ActiveRecord::Base
  has_one :address
  demeter_address

  def address_country
    @address_country ||= address.country.upcase
  end
end

To-Do

• Allow more than one level
• Automatically create accessors
• Detect all has_one and belongs_to relations and automatically "demeterized" them on ActiveRecord
• RDoc

Maintainer

• Emerson Macedo (http://codificando.com/)

Contributor

• Nando Vieira (http://simplesideias.com.br/)
• Tino Gomes (http://blog.tinogomes.com/)

License:

(The MIT License)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.