RhodeCode

/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library.

 *

 * Copyright (C) 2003-2008

 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

 * (Egervary Research Group on Combinatorial Optimization, EGRES).

 *

 * Permission to use, modify and distribute this software is granted

 * provided that this copyright notice appears in all copies. For

 * precise terms see the accompanying LICENSE file.

 *

 * This software is provided "AS IS" with no warranty of any kind,

 * express or implied, and with no claim as to its suitability for any

 * purpose.

 *

 */

/**

@defgroup datas Data Structures

This group describes the several data structures implemented in LEMON.

*/

/**

@defgroup graphs Graph Structures

@ingroup datas

\brief Graph structures implemented in LEMON.

The implementation of combinatorial algorithms heavily relies on

efficient graph implementations. LEMON offers data structures which are

planned to be easily used in an experimental phase of implementation studies,

and thereafter the program code can be made efficient by small modifications.

The most efficient implementation of diverse applications require the

usage of different physical graph implementations. These differences

appear in the size of graph we require to handle, memory or time usage

limitations or in the set of operations through which the graph can be

accessed.  LEMON provides several physical graph structures to meet

the diverging requirements of the possible users.  In order to save on

running time or on memory usage, some structures may fail to provide

some graph features like arc/edge or node deletion.

Alteration of standard containers need a very limited number of

operations, these together satisfy the everyday requirements.

In the case of graph structures, different operations are needed which do

not alter the physical graph, but gives another view. If some nodes or

arcs have to be hidden or the reverse oriented graph have to be used, then

this is the case. It also may happen that in a flow implementation

the residual graph can be accessed by another algorithm, or a node-set

is to be shrunk for another algorithm.

LEMON also provides a variety of graphs for these requirements called

\ref graph_adaptors "graph adaptors". Adaptors cannot be used alone but only

in conjunction with other graph representations.

You are free to use the graph structure that fit your requirements

the best, most graph algorithms and auxiliary data structures can be used

*/

/**

@defgroup semi_adaptors Semi-Adaptor Classes for Graphs

@ingroup graphs

\brief Graph types between real graphs and graph adaptors.

This group describes some graph types between real graphs and graph adaptors.

These classes wrap graphs to give new functionality as the adaptors do it.

On the other hand they are not light-weight structures as the adaptors.

*/

/**

@defgroup maps Maps

@ingroup datas

\brief Map structures implemented in LEMON.

This group describes the map structures implemented in LEMON.

new maps from existing ones.

*/

/**

@defgroup graph_maps Graph Maps

@ingroup maps

\brief Special graph-related maps.

This group describes maps that are specifically designed to assign

values to the nodes and arcs of graphs.

*/

/**

\defgroup map_adaptors Map Adaptors

\ingroup maps

\brief Tools to create new maps from existing ones

This group describes map adaptors that are used to create "implicit"

maps from other maps.

Most of them are \ref lemon::concepts::ReadMap "read-only maps".

They can make arithmetic and logical operations between one or two maps

(negation, shifting, addition, multiplication, logical 'and', 'or',

'not' etc.) or e.g. convert a map to another one of different Value type.

The typical usage of this classes is passing implicit maps to

algorithms.  If a function type algorithm is called then the function

type map adaptors can be used comfortable. For example let's see the

\code

  Color nodeColor(int deg) {

    if (deg >= 2) {

      return Color(0.5, 0.0, 0.5);

    } else if (deg == 1) {

      return Color(1.0, 0.5, 1.0);

    } else {

      return Color(0.0, 0.0, 0.0);

    }

  }

  Digraph::NodeMap<int> degree_map(graph);

    .coords(coords).scaleToA4().undirected()

    .nodeColors(composeMap(functorToMap(nodeColor), degree_map))

    .run();

\endcode

The \c functorToMap() function makes an \c int to \c Color map from the

and the previously created map. The composed map is a proper function to

get the color of each node.

The usage with class type algorithms is little bit harder. In this

case the function type map adaptors can not be used, because the

function map adaptors give back temporary objects.

\code

  Digraph graph;

  typedef Digraph::ArcMap<double> DoubleArcMap;

  DoubleArcMap length(graph);

  DoubleArcMap speed(graph);

  typedef DivMap<DoubleArcMap, DoubleArcMap> TimeMap;

  TimeMap time(length, speed);

  Dijkstra<Digraph, TimeMap> dijkstra(graph, time);

  dijkstra.run(source, target);

\endcode

We have a length map and a maximum speed map on the arcs of a digraph.

The minimum time to pass the arc can be calculated as the division of

the two maps which can be done implicitly with the \c DivMap template

class. We use the implicit minimum time map as the length map of the

\c Dijkstra algorithm.

*/

/**

@defgroup matrices Matrices

@ingroup datas

\brief Two dimensional data storages implemented in LEMON.

This group describes two dimensional data storages implemented in LEMON.

*/

/**

@defgroup paths Path Structures

@ingroup datas

\brief Path structures implemented in LEMON.

This group describes the path structures implemented in LEMON.

LEMON provides flexible data structures to work with paths.

All of them have similar interfaces and they can be copied easily with

assignment operators and copy constructors. This makes it easy and

efficient to have e.g. the Dijkstra algorithm to store its result in

any kind of path structure.

\sa lemon::concepts::Path

*/

/**

@defgroup auxdat Auxiliary Data Structures

@ingroup datas

\brief Auxiliary data structures implemented in LEMON.

This group describes some data structures implemented in LEMON in

order to make it easier to implement combinatorial algorithms.

*/

/**

@defgroup algs Algorithms

\brief This group describes the several algorithms

implemented in LEMON.

This group describes the several algorithms

implemented in LEMON.

*/

/**

@defgroup search Graph Search

@ingroup algs

\brief Common graph search algorithms.

This group describes the common graph search algorithms like

*/

/**

@ingroup algs

\brief Algorithms for finding shortest paths.

This group describes the algorithms for finding shortest paths in graphs.

*/

/**

@ingroup algs

\brief Algorithms for finding maximum flows.

This group describes the algorithms for finding maximum flows and

feasible circulations.

The maximum flow problem is to find a flow between a single source and

a single target that is maximum. Formally, there is a \f$G=(V,A)\f$

directed graph, an \f$c_a:A\rightarrow\mathbf{R}^+_0\f$ capacity

function and given \f$s, t \in V\f$ source and target node. The

maximum flow is the \f$f_a\f$ solution of the next optimization problem:

\f[ 0 \le f_a \le c_a \f]

\f[ \sum_{v\in\delta^{-}(u)}f_{vu}=\sum_{v\in\delta^{+}(u)}f_{uv}

\qquad \forall u \in V \setminus \{s,t\}\f]

\f[ \max \sum_{v\in\delta^{+}(s)}f_{uv} - \sum_{v\in\delta^{-}(s)}f_{vu}\f]

LEMON contains several algorithms for solving maximum flow problems:

- \ref lemon::EdmondsKarp "Edmonds-Karp"

- \ref lemon::Preflow "Goldberg's Preflow algorithm"

- \ref lemon::DinitzSleatorTarjan "Dinitz's blocking flow algorithm with dynamic trees"

- \ref lemon::GoldbergTarjan "Preflow algorithm with dynamic trees"

In most cases the \ref lemon::Preflow "Preflow" algorithm provides the

fastest method to compute the maximum flow. All impelementations

provides functions to query the minimum cut, which is the dual linear

programming problem of the maximum flow.

*/

/**

@ingroup algs

\brief Algorithms for finding minimum cost flows and circulations.

This group describes the algorithms for finding minimum cost flows and

circulations.

*/

/**

@ingroup algs

\brief Algorithms for finding minimum cut in graphs.

This group describes the algorithms for finding minimum cut in graphs.

The minimum cut problem is to find a non-empty and non-complete

\f$X\f$ subset of the vertices with minimum overall capacity on

outgoing arcs. Formally, there is \f$G=(V,A)\f$ directed graph, an

\f$c_a:A\rightarrow\mathbf{R}^+_0\f$ capacity function. The minimum

cut is the \f$X\f$ solution of the next optimization problem:

\f[ \min_{X \subset V, X\not\in \{\emptyset, V\}}

\sum_{uv\in A, u\in X, v\not\in X}c_{uv}\f]

LEMON contains several algorithms related to minimum cut problems:

- \ref lemon::HaoOrlin "Hao-Orlin algorithm" to calculate minimum cut

  in directed graphs

- \ref lemon::NagamochiIbaraki "Nagamochi-Ibaraki algorithm" to

  calculate minimum cut in undirected graphs

- \ref lemon::GomoryHuTree "Gomory-Hu tree computation" to calculate all

  pairs minimum cut in undirected graphs

If you want to find minimum cut just between two distinict nodes,

please see the \ref max_flow "Maximum Flow page".

*/

/**

@ingroup algs

\brief Algorithms for discovering the graph properties

This group describes the algorithms for discovering the graph properties

like connectivity, bipartiteness, euler property, simplicity etc.

\image html edge_biconnected_components.png

\image latex edge_biconnected_components.eps "bi-edge-connected components" width=\textwidth

*/

/**

@ingroup algs

\brief Algorithms for planarity checking, embedding and drawing

This group describes the algorithms for planarity checking,

embedding and drawing.

\image html planar.png

\image latex planar.eps "Plane graph" width=\textwidth

*/

/**

@ingroup algs

\brief Algorithms for finding matchings in graphs and bipartite graphs.

This group contains algorithm objects and functions to calculate

matchings in graphs and bipartite graphs. The general matching problem is

finding a subset of the arcs which does not shares common endpoints.

There are several different algorithms for calculate matchings in

graphs.  The matching problems in bipartite graphs are generally

easier than in general graphs. The goal of the matching optimization

can be the finding maximum cardinality, maximum weight or minimum cost

matching. The search can be constrained to find perfect or

maximum cardinality matching.

LEMON contains the next algorithms:

- \ref lemon::MaxBipartiteMatching "MaxBipartiteMatching" Hopcroft-Karp

  augmenting path algorithm for calculate maximum cardinality matching in

  bipartite graphs

- \ref lemon::PrBipartiteMatching "PrBipartiteMatching" Push-Relabel

  algorithm for calculate maximum cardinality matching in bipartite graphs

- \ref lemon::MaxWeightedBipartiteMatching "MaxWeightedBipartiteMatching"

  Successive shortest path algorithm for calculate maximum weighted matching

  and maximum weighted bipartite matching in bipartite graph

- \ref lemon::MinCostMaxBipartiteMatching "MinCostMaxBipartiteMatching"

  Successive shortest path algorithm for calculate minimum cost maximum

  matching in bipartite graph

- \ref lemon::MaxMatching "MaxMatching" Edmond's blossom shrinking algorithm

  for calculate maximum cardinality matching in general graph

- \ref lemon::MaxWeightedMatching "MaxWeightedMatching" Edmond's blossom

  shrinking algorithm for calculate maximum weighted matching in general

  graph

- \ref lemon::MaxWeightedPerfectMatching "MaxWeightedPerfectMatching"

  Edmond's blossom shrinking algorithm for calculate maximum weighted

  perfect matching in general graph

\image html bipartite_matching.png

\image latex bipartite_matching.eps "Bipartite Matching" width=\textwidth

*/

/**

@ingroup algs

\brief Algorithms for finding a minimum cost spanning tree in a graph.

This group describes the algorithms for finding a minimum cost spanning

tree in a graph

*/

/**

@ingroup algs

\brief Auxiliary algorithms implemented in LEMON.

This group describes some algorithms implemented in LEMON

in order to make it easier to implement complex algorithms.

*/

/**

\brief Approximation algorithms.

This group describes the approximation and heuristic algorithms

implemented in LEMON.

*/

/**

@defgroup gen_opt_group General Optimization Tools

\brief This group describes some general optimization frameworks

implemented in LEMON.

This group describes some general optimization frameworks

implemented in LEMON.

*/

/**

@ingroup gen_opt_group

\brief Lp and Mip solver interfaces for LEMON.

This group describes Lp and Mip solver interfaces for LEMON. The

various LP solvers could be used in the same manner with this

interface.

*/

/**

@ingroup lp_group

\brief Helper tools to the Lp and Mip solvers.

This group adds some helper tools to general optimization framework

implemented in LEMON.

*/

/**

@defgroup metah Metaheuristics

@ingroup gen_opt_group

\brief Metaheuristics for LEMON library.

This group describes some metaheuristic optimization tools.

*/

/**

@defgroup utils Tools and Utilities

\brief Tools and utilities for programming in LEMON

Tools and utilities for programming in LEMON.

*/

/**

@defgroup gutils Basic Graph Utilities

@ingroup utils

\brief Simple basic graph utilities.

This group describes some simple basic graph utilities.

*/

/**

@defgroup misc Miscellaneous Tools

@ingroup utils

\brief Tools for development, debugging and testing.

This group describes several useful tools for development,

debugging and testing.

*/

/**

@ingroup misc

\brief Simple tools for measuring the performance of algorithms.

This group describes simple tools for measuring the performance

of algorithms.

*/

/**

@defgroup exceptions Exceptions

@ingroup utils

\brief Exceptions defined in LEMON.

This group describes the exceptions defined in LEMON.

*/

/**

@defgroup io_group Input-Output

\brief Graph Input-Output methods

This group describes the tools for importing and exporting graphs

*/

/**

@defgroup lemon_io LEMON Input-Output

@ingroup io_group

This group describes methods for reading and writing

\ref lgf-format "LEMON Graph Format".

*/

/**

@ingroup io_group

\brief General \c EPS drawer and graph exporter

This group describes general \c EPS drawing methods and special

graph exporting tools.

*/

/**

@defgroup concept Concepts

\brief Skeleton classes and concept checking classes

This group describes the data/algorithm skeletons and concept checking

classes implemented in LEMON.

The purpose of the classes in this group is fourfold.

- These classes contain the documentations of the concepts. In order

  to avoid document multiplications, an implementation of a concept

  simply refers to the corresponding concept class.

- These classes declare every functions, <tt>typedef</tt>s etc. an

  implementation of the concepts should provide, however completely

  without implementations and real data structures behind the

  interface. On the other hand they should provide nothing else. All

  the algorithms working on a data structure meeting a certain concept

  should compile with these classes. (Though it will not run properly,

  of course.) In this way it is easily to check if an algorithm

  doesn't use any extra feature of a certain implementation.

- The concept descriptor classes also provide a <em>checker class</em>

  that makes it possible to check whether a certain implementation of a

  concept indeed provides all the required features.

- Finally, They can serve as a skeleton of a new implementation of a concept.

*/

/**

@defgroup graph_concepts Graph Structure Concepts

@ingroup concept

\brief Skeleton and concept checking classes for graph structures

This group describes the skeletons and concept checking classes of LEMON's

graph structures and helper classes used to implement these.

*/

*/

/**

\anchor demoprograms

@defgroup demos Demo programs

Some demo programs are listed here. Their full source codes can be found in

the \c demo subdirectory of the source tree.

It order to compile them, use <tt>--enable-demo</tt> configure option when

build the library.

*/

/**

@defgroup tools Standalone utility applications

Some utility applications are listed here.

The standard compilation procedure (<tt>./configure;make</tt>) will compile

them, as well.

*/

/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library.

 *

 * Copyright (C) 2003-2008

 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

 * (Egervary Research Group on Combinatorial Optimization, EGRES).

 *

 * Permission to use, modify and distribute this software is granted

 * provided that this copyright notice appears in all copies. For

 * precise terms see the accompanying LICENSE file.

 *

 * This software is provided "AS IS" with no warranty of any kind,

 * express or implied, and with no claim as to its suitability for any

 * purpose.

 *

 */

/**

\mainpage LEMON Documentation

\section intro Introduction

\subsection whatis What is LEMON

LEMON stands for

<b>L</b>ibrary of <b>E</b>fficient <b>M</b>odels

and <b>O</b>ptimization in <b>N</b>etworks.

It is a C++ template

library aimed at combinatorial optimization tasks which

often involve in working

with graphs.

<b>

LEMON is an <a class="el" href="http://opensource.org/">open&nbsp;source</a>

project.

You are free to use it in your commercial or

non-commercial applications under very permissive

\ref license "license terms".

</b>

\subsection howtoread How to read the documentation

If you want to get a quick start and see the most important features then

take a look at our \ref quicktour

"Quick Tour to LEMON" which will guide you along.

If you already feel like using our library, see the page that tells you

\ref getstart "How to start using LEMON".

If you

want to see how LEMON works, see

If you know what you are looking for then try to find it under the

<a class="el" href="modules.html">Modules</a>

section.

*/

/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library.

 *

 * Copyright (C) 2003-2008

 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

 * (Egervary Research Group on Combinatorial Optimization, EGRES).

 *

 * Permission to use, modify and distribute this software is granted

 * provided that this copyright notice appears in all copies. For

 * precise terms see the accompanying LICENSE file.

 *

 * This software is provided "AS IS" with no warranty of any kind,

 * express or implied, and with no claim as to its suitability for any

 * purpose.

 *

 */

namespace lemon {

/*!

\page migration Migration from the 0.x Series

This guide gives an in depth description on what has changed compared

to the 0.x release series.

Many of these changes adjusted automatically by the

<tt>script/lemon-0.x-to-1.x.sh</tt> tool. Those requiring manual

update are typeset <b>boldface</b>.

\section migration-graph Graph Related Name Changes

- \ref concepts::Digraph "Directed graphs" are called \c Digraph and

  they have <tt>Arc</tt>s (instead of <tt>Edge</tt>s), while

  \ref concepts::Graph "undirected graphs" are called \c Graph

  (instead of \c UGraph) and they have <tt>Edge</tt>s (instead of

  <tt>UEdge</tt>s). These changes reflected thoroughly everywhere in

  the library. Namely,

  - \c Graph -> \c Digraph

    - \c %ListGraph -> \c ListDigraph, \c %SmartGraph -> \c SmartDigraph etc.

  - \c UGraph -> \c Graph

    - \c ListUGraph -> \c ListGraph, \c SmartUGraph -> \c SmartGraph etc.

  - \c Edge -> \c Arc, \c UEdge -> \c Edge

  - \c EdgeMap -> \c ArcMap, \c UEdgeMap -> \c EdgeMap

  - \c EdgeIt -> \c ArcIt, \c UEdgeIt -> \c EdgeIt

  - Class names and function names containing the words \c graph,

    \c ugraph, \e edge or \e arc should also be updated.

- <b>The two endpoints of an (\e undirected) \c Edge can be obtained by the

  <tt>u()</tt> and <tt>v()</tt> member function of the graph

  (instead of <tt>source()</tt> and <tt>target()</tt>). This change

  must be done by hand.</b>

  \n Of course, you can still use <tt>source()</tt> and <tt>target()</tt>

  for <tt>Arc</tt>s (directed edges).

\warning

<b>The <tt>script/lemon-0.x-to-1.x.sh</tt> tool replaces all instances of

the words \c graph, \c digraph, \c edge and \c arc, so it replaces them

in strings, comments etc. as well as in all identifiers.</b>

 - The \ref lgf-format "LGF file format" has changed,

   <tt>\@nodeset</tt> has changed to <tt>\@nodes</tt>,

   <tt>\@edgeset</tt> and <tt>\@uedgeset</tt> to <tt>\@arcs</tt> or

   <tt>\@edges</tt>, which become completely equivalents. The

   <tt>\@nodes</tt>, <tt>\@edges</tt> and <tt>\@uedges</tt> sections are

   removed from the format, the content of them should be

   the part of <tt>\@attributes</tt> section. The data fields in

   the sections must follow a strict format, they must be either character

   sequences without whitespaces or quoted strings.

 - The <tt>LemonReader</tt> and <tt>LemonWriter</tt> core interfaces

   are no longer available.

 - The implementation of the general section readers and writers has changed

   they are simple functors now. Beside the old

   stream based section handling, currently line oriented section

   reading and writing are also supported. In the

   section readers the lines must be counted manually. The sections

   should be read and written with the SectionWriter and SectionReader

   classes.

 - Instead of the item readers and writers, item converters should be

   used. The converters are functors, which map the type to

   std::string or std::string to the type. The converters for standard

   containers hasn't yet been implemented in the new LEMON. The converters

   can return strings in any format, because if it is necessary, the LGF

   writer and reader will quote and unquote the given value.

 - The DigraphReader and DigraphWriter can used similarly to the

   0.x series, however the <tt>read</tt> or <tt>write</tt> prefix of

   the member functions are removed.

 - The new LEMON supports the function like interface, the \c

   digraphReader and \c digraphWriter functions are more convenient than

   using the classes directly.

\section migration-search BFS, DFS and Dijkstra

- <b>Using the function interface of BFS, DFS and %Dijkstra both source and

  target nodes can be given as parameters of the <tt>run()</tt> function

  (instead of \c bfs(), \c dfs() or \c dijkstra() itself).</b>

- \ref named-templ-param "Named class template parameters" of \c Bfs,

  \c Dfs, \c Dijkstra, \c BfsVisit, \c DfsVisit are renamed to start

  with "Set" instead of "Def". Namely,

  - \c DefPredMap -> \c SetPredMap

  - \c DefDistMap -> \c SetDistMap

  - \c DefReachedMap -> \c SetReachedMap

  - \c DefProcessedMap -> \c SetProcessedMap

  - \c DefHeap -> \c SetHeap

  - \c DefStandardHeap -> \c SetStandardHeap

  - \c DefOperationTraits -> \c SetOperationTraits

  - \c DefProcessedMapToBeDefaultMap -> \c SetStandardProcessedMap

\section migration-error Exceptions and Debug tools

<b>The class hierarchy of exceptions has largely been simplified. Now,

only the i/o related tools may throw exceptions. All other exceptions

have been replaced with either the \c LEMON_ASSERT or the \c LEMON_DEBUG

macros.</b>

<b>On the other hand, the parameter order of constructors of the

exceptions has been changed. See \ref IoError and \ref FormatError for

more details.</b>

\section migration-other Others

- <b>The contents of <tt>graph_utils.h</tt> are moved to <tt>core.h</tt>

  and <tt>maps.h</tt>. <tt>core.h</tt> is included by all graph types,

  therefore it usually do not have to be included directly.</b>

- <b><tt>path_utils.h</tt> is merged to \c path.h.</b>

- <b>The semantic of the assignment operations and copy constructors of maps

  are still under discussion. So, you must copy them by hand (i.e. copy

  each entry one-by-one)</b>

- <b>The parameters of the graph copying tools (i.e. \c GraphCopy,

  \c DigraphCopy) have to be given in the from-to order.</b>

- \c copyDigraph() and \c copyGraph() are renamed to \c digraphCopy()

  and \c graphCopy(), respectively.

- <b>The interface of \ref DynArcLookUp has changed. It is now the same as

  of \ref ArcLookUp and \ref AllArcLookUp</b>

- Some map types should also been renamed. Namely,

  - \c IntegerMap -> \c RangeMap

  - \c StdMap -> \c SparseMap

  - \c FunctorMap -> \c FunctorToMap

  - \c MapFunctor -> \c MapToFunctor

  - \c ForkWriteMap -> \c ForkMap

  - \c StoreBoolMap -> \c LoggerBoolMap

- \c dim2::BoundingBox -> \c dim2::Box

*/

}

/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library.

 *

 * Copyright (C) 2003-2008

 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

 * (Egervary Research Group on Combinatorial Optimization, EGRES).

 *

 * Permission to use, modify and distribute this software is granted

 * provided that this copyright notice appears in all copies. For

 * precise terms see the accompanying LICENSE file.

 *

 * This software is provided "AS IS" with no warranty of any kind,

 * express or implied, and with no claim as to its suitability for any

 * purpose.

 *

 */

#ifndef LEMON_BITS_ALTERATION_NOTIFIER_H

#define LEMON_BITS_ALTERATION_NOTIFIER_H

#include <vector>

#include <list>

#include <lemon/core.h>

namespace lemon {

  template <typename _Container, typename _Item>

  class AlterationNotifier {

  public:

    typedef True Notifier;

    typedef _Container Container;

    typedef _Item Item;

    struct ImmediateDetach {};

    class ObserverBase {

    protected:

      typedef AlterationNotifier Notifier;

      friend class AlterationNotifier;

      ObserverBase() : _notifier(0) {}

      ObserverBase(AlterationNotifier& nf) {

        attach(nf);

      }

      ObserverBase(const ObserverBase& copy) {

        if (copy.attached()) {

          attach(*copy.notifier());

        }

      }

      virtual ~ObserverBase() {

        if (attached()) {

          detach();

        }

      }

      void attach(AlterationNotifier& nf) {

        nf.attach(*this);

      }