module Roda::RodaPlugins::Flash::InstanceMethods

def _roda_after_40__flash(_)

hash in the session so the next request has access to it.
If the routing doesn't raise an error, rotate the flash
def _roda_after_40__flash(_)
  if f = @_flash
    f = f.next
    if f.empty?
      session.delete('_flash')
    else
      session['_flash'] = f
    end
  end
end