[shared] array/hash support for system_settings

https://github.com/realityforge/rails-system-settings

# system_settings/lib/system_setting.rb

class SystemSetting < ActiveRecord::Base
  @@data = {}

  validates_length_of :name, :in => 1..255
  validates_uniqueness_of :name

  serialize :value

  def self.[](name)
    name = name.to_s unless name.is_a? String
    return @@data[name] unless @@data[name].nil?
    p = SystemSetting.find_by_name(name)
    @@data[name] = p ? p.value.freeze : nil
  end

  def self.[]=(name, value)
    name = name.to_s unless name.is_a? String
    p = SystemSetting.find_or_initialize_by_name(name)
    @@data[name] = p.value = value
    p.save!
    p.value.freeze
  end
end