Perpetuity::Mapper idea

mapper.rb

require 'set'

class Mapper
  def initialize
    self.class.base_class.add_mapper self.class
  end

  def self.mappers
    @mappers ||= Set.new
  end

  def self.[] klass
    base_class.models[klass].new
  end

  def self.model klass
    base_class.models[klass] = self
    base_class.add_mapper self
  end

  def self.models
    @models ||= Hash.new do
      raise "No mapper for class '#{klass}'"
    end
  end

  def self.add_mapper mapper
    base_class.mappers << mapper
  end

  def self.base_class
    Mapper
  end
end

Article = Class.new
class ArticleMapper < Mapper
  model Article
end

User = Class.new
class UserMapper < Mapper
  model User
end

Comment = Class.new
class CommentMapper < Mapper
  model Comment
end