content_for in controller as described in http://blog.yakitara.com/2011/05/rails-31-http-streaming-and-contentfor.html

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

Simple hack to make it work with a block - just do @_content_for||=yield

I cut-pasted this to make provide for controllers - https://gist.github.com/hiroshi/985457

While this gist comes handy, it's too much just to use it to change the page titles. If someone wants to use this gist just to change the title of the pages dynamically it would be better just to put the following in the layout:

<title><%= @title || "default title" %></title>

With that approach one will just have to set the @title instance variable in the controller, like this:

@title = 'My title'

Sorry to stir up an old topic, but what about memoizing the view_context? Will that cause other issues? Seems to work for me in rails 4.

  def view_context
    @view_context ||= super
  end
  delegate :content_for, to: :view_context

EDIT
Found out real quick: Don't do this, it breaks instance variable assignment...

seems broken on rails 4