gistfile1.rb

class ApplicationController < ActionController::Base
  ...
  # FORCE to implement content_for in controller
  def view_context
    super.tap do |view|
      (@_content_for || {}).each do |name,content|
        view.content_for name, content
      end
    end
  end
  def content_for(name, content) # no blocks allowed yet
    @_content_for ||= {}
    if @_content_for[name].respond_to?(:<<)
      @_content_for[name] << content
    else
      @_content_for[name] = content
    end
  end
  def content_for?(name)
    @_content_for[name].present?
  end
end

gistfile2.rb

class PostsController < ApplicationController
  def index
    content_for :title, "List of posts"
    ...
  end
end