Source: ../../policy/common/element_factory.hh
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// -*- c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t -*-
// vim:set sts=4 ts=8:
// Copyright (c) 2001-2005 International Computer Science Institute
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software")
// to deal in the Software without restriction, subject to the conditions
// listed in the XORP LICENSE file. These conditions include: you must
// preserve this copyright notice, and you cannot mention the copyright
// holders in advertising related to the Software without their permission.
// The Software is provided WITHOUT ANY WARRANTY, EXPRESS OR IMPLIED. This
// notice is a summary of the XORP LICENSE file; the license in that file is
// legally binding.
// $XORP: xorp/policy/common/element_factory.hh,v 1.3 2005/07/15 02:27:09 abittau Exp $
#ifndef __POLICY_COMMON_ELEMENT_FACTORY_HH__
#define __POLICY_COMMON_ELEMENT_FACTORY_HH__
#include <map>
#include <string>
#include <sstream>
#include "register_elements.hh"
#include "element_base.hh"
#include "elem_set.hh"
#include "policy_exception.hh"
/**
* @short A factory for creating elements based on their type.
*
* Elements are created via their string represented type. They are initialized
* via a c-style string. If this string is null, then a default value is
* assigned to the element.
*
* Functions that perform the creation are registered with the factory at
* run-time.
*
* An exception is throw on element creationg failure.
*
* Similar to Dispatcher.
*/
class ElementFactory {
public:
// Function called to create element
typedef Element* (*Callback)(const char*);
// Container which maps a key to a callback. May consider using a hash table.
typedef map<string,Callback> Map;
ElementFactory();
/**
* @short Exception thrown if an Unknown element is being created.
*
* When creating an element of a type which has no registered creation
* callback with the factory.
*/
class UnknownElement : public PolicyException {
public:
UnknownElement(const string& elem) :
PolicyException("ElementFactory: unable to create unknown element: " + elem) {}
};
/**
* Register a callback with the factory.
*
* @param key the element id/type. Must be unique.
* @param cb function to be called when the element must be created.
*/
void add(const string& key, Callback cb);
/**
* Create an element.
*
* @return the requested element. Caller is responsible for deletion.
* @param key the type of element that needs to be created.
* @param arg initial value of element. If null, a default is assigned.
*/
Element* create(const string& key, const char* arg);
/**
* Checks whether a type exists.
*
* @param key the element to check for.
* @return true if the element can be create via the factory.
*/
static bool can_create(const string& key);
private:
/**
* There is only one factory map.
*
* Creating additional factory objects is therefore safe. No need to pass a
* global factory around in the various classes.
*/
static Map _map;
/**
* A class which registers defined callbacks upon creation.
*
* Callbacks are thus registered once [static] and before the factory is
* actually used.
*/
static RegisterElements _regelems;
};
#endif // __POLICY_COMMON_ELEMENT_FACTORY_HH__
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