module Roda::RodaPlugins::Flash::InstanceMethods

def call

hash in the session so the next request has access to it.
If the routing doesn't raise an error, rotate the flash 
def call
  res = super
  if f = @_flash
    session[KEY] = f.next
  end
  res
end

def flash

it from the session if it is not already loaded.
Access the flash hash for the current request, loading 
def flash
  @_flash ||= FlashHash.new(session[KEY])
end