How to pass a variable to a layout?

Question

I have a two versions of my application layout, which are differs only in a few lines. Consider following example:

!!!    
%html
    %head
        # a lot of cod         


        

Answer 1

Okay, so I found the solution by myself:

class ApplicationController < ActionController::Base
    layout 'layout'
    before_filter :set_constants

    def set_constants
        @flag = true
    end
end

And the template should be:

!!!    
%html
    %head
        # a lot of code here
%body
    # some more code here
    - if @flag
        # variant 1
    - else
        # variant 2