class Google::Protobuf::FieldDescriptor

def set(msg, value)
  if msg.class.descriptor != Google::Protobuf::FFI.get_containing_message_def(self)
    raise TypeError.new "set method called on wrong message type"
  end
  unless set_value_on_message value, msg.instance_variable_get(:@msg), msg.instance_variable_get(:@arena)
    raise RuntimeError.new "allocation failed"
  end
  nil
end