*gist*

class Trait < Module
  def self.new(&blk)
    m = super{ } # note: passing empty block overrides &blk
    class << m
      include ClassMethods
    end
    m.deferred_block = blk
    m
  end

  module ClassMethods
    attr_accessor :deferred_block
    def included(mod)
      mod.class_eval(&@deferred_block)
    end
  end
end


module Traits
  Comment = Trait.new do
    #
    # Behaviors
    #

    include ::DataMapper::Resource

    #
    # Properties
    #

    include ::Traits::UserGeneratedContent

    #
    # Associations
    #

    belong_to parent_association_name

    #
    # Validations
    #

    validates_present parent_association_name
    
    #
    # API
    #

    def recent?
      # ...
    end

    def by_author?
      # ...
    end

    def reply?
      # ...
    end
  end
end


class MessageComment
  def self.parent_association_name
    :message
  end
  
  include ::Traits::Comment
end


class ArticleComment
  def self.parent_association_name
    :article
  end
  
  include ::Traits::Comment
end


class TicketComment
  def self.parent_association_name
    :ticket
  end
  
  include ::Traits::Comment

  #
  # API
  #

  def by_staff_member?
    # ...
  end
end