// -*- c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t -*- // vim:set sts=4 ts=8: // Copyright (c) 2001-2009 XORP, Inc. // // This program is free software; you can redistribute it and/or modify // it under the terms of the GNU General Public License, Version 2, June // 1991 as published by the Free Software Foundation. Redistribution // and/or modification of this program under the terms of any other // version of the GNU General Public License is not permitted. // // This program is distributed in the hope that it will be useful, but // WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. For more details, // see the GNU General Public License, Version 2, a copy of which can be // found in the XORP LICENSE.gpl file. // // XORP Inc, 2953 Bunker Hill Lane, Suite 204, Santa Clara, CA 95054, USA; // http://xorp.net // $XORP: xorp/policy/common/elem_null.hh,v 1.11 2009/01/05 18:31:06 jtc Exp $ #ifndef __POLICY_COMMON_ELEM_NULL_HH__ #define __POLICY_COMMON_ELEM_NULL_HH__ #include "element_base.hh" #include <string> /** * @short An element representing nothing. Null. * * This is used by VarRW when an element being read is not available. For * example, if the route is IPv4, but the IPv6 representation is being asked * for. * * The dispatcher also treats Null arguments as a special case by returning a * Null. */ class ElemNull : public Element { public: static const char* id; static Hash _hash; ElemNull() : Element(_hash) {} ElemNull(const char* /* c_str */) : Element(_hash) {} string str() const { return "null"; } const char* type() const { return id; } }; #endif // __POLICY_COMMON_ELEM_NULL_HH__