select_layout实现Ruby元编程

class Cpu::ContextsController < Cpu::ApplicationController

  layout :select_layout

  private

  def has_resource?
    true # dummy
  end

  def select_layout
    has_resource? ? \'cpu/context\' : \'cpu/account\'
  end
end

class Cpu::ContextsController < Cpu::ApplicationController
  select_layout do
    has_resource? ? \'cpu/context\' : \'cpu/account\'
  end
end

  before_filter do
    self.class.send(:layout, has_resource? ? \'cpu/context\' : \'cpu/account\')
  end

render ..., :layout => has_resource? ? \"cpu/context\" : \"cpu/account\"

layout