# lib/link_bar.rb
require 'singleton'

class LinkBar
  include Singleton

  class << self
    def register(callback)
      instance.register(callback)
    end
    
    def query(link_name)
      instance.query(link_name)
    end
  end
  
  def initialize
    @callbacks = []
  end
  
  def register(callback)
    @callbacks << callback
  end
  
  def query(link_name)
    returning Array.new do |arr|
      @callbacks.each do |callback|
        arr << callback.call(link_name)
      end
    end.flatten.uniq
  end
end

# vendor/plugins/<name>/init.rb
LinkBar.register(<Name>.method(:link_generation))

# vendor/plugins/<name>/lib/<name>.rb
class <Name>
  def self.link_generation(link_name)
    case link_name
    when "boards"
      [boards_url, "#{link_name} Boards"]
    when "other"
      [other_url, "#{link_name} Other"]
    end
  end
end

# app/controllers/some_controller.rb
class SomeController
  before_filter :find_board_links
  
  def find_board_links
    @board_links = LinkBar.query("boards")
  end
end