http://blog.danieroux.com/2008/12/29/dynamic-tasks-with-rake-namespaces

Rakefile.rb

# Supporting class for demo purposes
class DatabaseStub
  attr_reader :name
 
  def self.instances
    ["development", "test", "ci"]
  end

  def initialize(databaseName)
    @name = databaseName
  end
 
  def running?
    @name == "development"
  end
 
  def method_missing(sym, *args, &block)
    puts "Action '#{sym}' would now be performed on database '#@name'"
  end
end
 
# Define our own task type
def task_database(database, action)
  desc "#{action.to_s} - #{database.name}"
  task action do
    # Use message sending to just pass on the action to the
    # instance.
    database.send(action)
  end
end
 
# Define the tasks
DatabaseStub.instances.each do |databaseName|
  namespace databaseName do
    database = DatabaseStub.new(databaseName)
 
    task_database(database, :status)
    task_database(database, :restart)
 
    if database.running?
      task_database(database, :stop)
    else
      task_database(database, :start)
    end
 
  end
end