Non-expiring flash

gistfile1.txt

# Visit:
# /main/set_flash
# /main/show_no_flash (as many times as you like)
# /main/show_flash ... and it shows the flash message
# (Rails 4.1.8, Ruby 2.1.1)

# app/controllers/main_controller.rb
class MainController < ApplicationController
  def show_flash
    render inline: flash[:notice] || "Flash is blank!"
  end

  def set_flash
    flash[:notice] = "FLASH!"
    render inline: "Nothing to see here"
  end

  def show_no_flash
    render inline: "Nothing to see here"
  end
end

# config/routes.rb
Rails.application.routes.draw do
  get 'main/set_flash'
  get 'main/show_flash'
  get 'main/show_no_flash'
end