module Rack::Request::Helpers

def delete_param(k)

env['rack.input'] is not touched.

If the parameter is in both GET and POST, the POST value takes precedence since that's how #params works.

Destructively delete a parameter, whether it's in GET or POST. Returns the value of the deleted parameter. 
def delete_param(k)
  post_value, get_value = self.POST.delete(k), self.GET.delete(k)
  post_value || get_value
end