lemon/smart_graph.h
changeset 782 ceb2756dea2a
parent 778 a143f19f465b
parent 736 2e20aad15754
child 787 c2230649a493
     1.1 --- a/lemon/smart_graph.h	Mon Sep 28 15:53:20 2009 +0200
     1.2 +++ b/lemon/smart_graph.h	Thu Nov 05 10:27:17 2009 +0100
     1.3 @@ -32,10 +32,7 @@
     1.4  namespace lemon {
     1.5  
     1.6    class SmartDigraph;
     1.7 -  ///Base of SmartDigraph
     1.8  
     1.9 -  ///Base of SmartDigraph
    1.10 -  ///
    1.11    class SmartDigraphBase {
    1.12    protected:
    1.13  
    1.14 @@ -187,28 +184,26 @@
    1.15    ///
    1.16    ///\brief A smart directed graph class.
    1.17    ///
    1.18 -  ///This is a simple and fast digraph implementation.
    1.19 -  ///It is also quite memory efficient, but at the price
    1.20 -  ///that <b> it does support only limited (only stack-like)
    1.21 -  ///node and arc deletions</b>.
    1.22 -  ///It fully conforms to the \ref concepts::Digraph "Digraph concept".
    1.23 +  ///\ref SmartDigraph is a simple and fast digraph implementation.
    1.24 +  ///It is also quite memory efficient but at the price
    1.25 +  ///that it does not support node and arc deletion 
    1.26 +  ///(except for the Snapshot feature).
    1.27    ///
    1.28 -  ///\sa concepts::Digraph.
    1.29 +  ///This type fully conforms to the \ref concepts::Digraph "Digraph concept"
    1.30 +  ///and it also provides some additional functionalities.
    1.31 +  ///Most of its member functions and nested classes are documented
    1.32 +  ///only in the concept class.
    1.33 +  ///
    1.34 +  ///\sa concepts::Digraph
    1.35 +  ///\sa SmartGraph
    1.36    class SmartDigraph : public ExtendedSmartDigraphBase {
    1.37      typedef ExtendedSmartDigraphBase Parent;
    1.38  
    1.39    private:
    1.40 -
    1.41 -    ///SmartDigraph is \e not copy constructible. Use DigraphCopy() instead.
    1.42 -
    1.43 -    ///SmartDigraph is \e not copy constructible. Use DigraphCopy() instead.
    1.44 -    ///
    1.45 +    /// Digraphs are \e not copy constructible. Use DigraphCopy instead.
    1.46      SmartDigraph(const SmartDigraph &) : ExtendedSmartDigraphBase() {};
    1.47 -    ///\brief Assignment of SmartDigraph to another one is \e not allowed.
    1.48 -    ///Use DigraphCopy() instead.
    1.49 -
    1.50 -    ///Assignment of SmartDigraph to another one is \e not allowed.
    1.51 -    ///Use DigraphCopy() instead.
    1.52 +    /// \brief Assignment of a digraph to another one is \e not allowed.
    1.53 +    /// Use DigraphCopy instead.
    1.54      void operator=(const SmartDigraph &) {}
    1.55  
    1.56    public:
    1.57 @@ -221,79 +216,49 @@
    1.58  
    1.59      ///Add a new node to the digraph.
    1.60  
    1.61 -    /// Add a new node to the digraph.
    1.62 -    /// \return The new node.
    1.63 +    ///This function adds a new node to the digraph.
    1.64 +    ///\return The new node.
    1.65      Node addNode() { return Parent::addNode(); }
    1.66  
    1.67      ///Add a new arc to the digraph.
    1.68  
    1.69 -    ///Add a new arc to the digraph with source node \c s
    1.70 +    ///This function adds a new arc to the digraph with source node \c s
    1.71      ///and target node \c t.
    1.72      ///\return The new arc.
    1.73 -    Arc addArc(const Node& s, const Node& t) {
    1.74 +    Arc addArc(Node s, Node t) {
    1.75        return Parent::addArc(s, t);
    1.76      }
    1.77  
    1.78 -    /// \brief Using this it is possible to avoid the superfluous memory
    1.79 -    /// allocation.
    1.80 -
    1.81 -    /// Using this it is possible to avoid the superfluous memory
    1.82 -    /// allocation: if you know that the digraph you want to build will
    1.83 -    /// be very large (e.g. it will contain millions of nodes and/or arcs)
    1.84 -    /// then it is worth reserving space for this amount before starting
    1.85 -    /// to build the digraph.
    1.86 -    /// \sa reserveArc
    1.87 -    void reserveNode(int n) { nodes.reserve(n); };
    1.88 -
    1.89 -    /// \brief Using this it is possible to avoid the superfluous memory
    1.90 -    /// allocation.
    1.91 -
    1.92 -    /// Using this it is possible to avoid the superfluous memory
    1.93 -    /// allocation: if you know that the digraph you want to build will
    1.94 -    /// be very large (e.g. it will contain millions of nodes and/or arcs)
    1.95 -    /// then it is worth reserving space for this amount before starting
    1.96 -    /// to build the digraph.
    1.97 -    /// \sa reserveNode
    1.98 -    void reserveArc(int m) { arcs.reserve(m); };
    1.99 -
   1.100      /// \brief Node validity check
   1.101      ///
   1.102 -    /// This function gives back true if the given node is valid,
   1.103 -    /// ie. it is a real node of the graph.
   1.104 +    /// This function gives back \c true if the given node is valid,
   1.105 +    /// i.e. it is a real node of the digraph.
   1.106      ///
   1.107      /// \warning A removed node (using Snapshot) could become valid again
   1.108 -    /// when new nodes are added to the graph.
   1.109 +    /// if new nodes are added to the digraph.
   1.110      bool valid(Node n) const { return Parent::valid(n); }
   1.111  
   1.112      /// \brief Arc validity check
   1.113      ///
   1.114 -    /// This function gives back true if the given arc is valid,
   1.115 -    /// ie. it is a real arc of the graph.
   1.116 +    /// This function gives back \c true if the given arc is valid,
   1.117 +    /// i.e. it is a real arc of the digraph.
   1.118      ///
   1.119      /// \warning A removed arc (using Snapshot) could become valid again
   1.120 -    /// when new arcs are added to the graph.
   1.121 +    /// if new arcs are added to the graph.
   1.122      bool valid(Arc a) const { return Parent::valid(a); }
   1.123  
   1.124 -    ///Clear the digraph.
   1.125 -
   1.126 -    ///Erase all the nodes and arcs from the digraph.
   1.127 -    ///
   1.128 -    void clear() {
   1.129 -      Parent::clear();
   1.130 -    }
   1.131 -
   1.132      ///Split a node.
   1.133  
   1.134 -    ///This function splits a node. First a new node is added to the digraph,
   1.135 -    ///then the source of each outgoing arc of \c n is moved to this new node.
   1.136 -    ///If \c connect is \c true (this is the default value), then a new arc
   1.137 -    ///from \c n to the newly created node is also added.
   1.138 +    ///This function splits the given node. First, a new node is added
   1.139 +    ///to the digraph, then the source of each outgoing arc of node \c n
   1.140 +    ///is moved to this new node.
   1.141 +    ///If the second parameter \c connect is \c true (this is the default
   1.142 +    ///value), then a new arc from node \c n to the newly created node
   1.143 +    ///is also added.
   1.144      ///\return The newly created node.
   1.145      ///
   1.146 -    ///\note The <tt>Arc</tt>s
   1.147 -    ///referencing a moved arc remain
   1.148 -    ///valid. However <tt>InArc</tt>'s and <tt>OutArc</tt>'s
   1.149 -    ///may be invalidated.
   1.150 +    ///\note All iterators remain valid.
   1.151 +    ///
   1.152      ///\warning This functionality cannot be used together with the Snapshot
   1.153      ///feature.
   1.154      Node split(Node n, bool connect = true)
   1.155 @@ -308,6 +273,34 @@
   1.156        return b;
   1.157      }
   1.158  
   1.159 +    ///Clear the digraph.
   1.160 +
   1.161 +    ///This function erases all nodes and arcs from the digraph.
   1.162 +    ///
   1.163 +    void clear() {
   1.164 +      Parent::clear();
   1.165 +    }
   1.166 +
   1.167 +    /// Reserve memory for nodes.
   1.168 +
   1.169 +    /// Using this function, it is possible to avoid superfluous memory
   1.170 +    /// allocation: if you know that the digraph you want to build will
   1.171 +    /// be large (e.g. it will contain millions of nodes and/or arcs),
   1.172 +    /// then it is worth reserving space for this amount before starting
   1.173 +    /// to build the digraph.
   1.174 +    /// \sa reserveArc()
   1.175 +    void reserveNode(int n) { nodes.reserve(n); };
   1.176 +
   1.177 +    /// Reserve memory for arcs.
   1.178 +
   1.179 +    /// Using this function, it is possible to avoid superfluous memory
   1.180 +    /// allocation: if you know that the digraph you want to build will
   1.181 +    /// be large (e.g. it will contain millions of nodes and/or arcs),
   1.182 +    /// then it is worth reserving space for this amount before starting
   1.183 +    /// to build the digraph.
   1.184 +    /// \sa reserveNode()
   1.185 +    void reserveArc(int m) { arcs.reserve(m); };
   1.186 +
   1.187    public:
   1.188  
   1.189      class Snapshot;
   1.190 @@ -332,20 +325,23 @@
   1.191  
   1.192    public:
   1.193  
   1.194 -    ///Class to make a snapshot of the digraph and to restrore to it later.
   1.195 +    ///Class to make a snapshot of the digraph and to restore it later.
   1.196  
   1.197 -    ///Class to make a snapshot of the digraph and to restrore to it later.
   1.198 +    ///Class to make a snapshot of the digraph and to restore it later.
   1.199      ///
   1.200      ///The newly added nodes and arcs can be removed using the
   1.201 -    ///restore() function.
   1.202 -    ///\note After you restore a state, you cannot restore
   1.203 -    ///a later state, in other word you cannot add again the arcs deleted
   1.204 -    ///by restore() using another one Snapshot instance.
   1.205 +    ///restore() function. This is the only way for deleting nodes and/or
   1.206 +    ///arcs from a SmartDigraph structure.
   1.207      ///
   1.208 -    ///\warning If you do not use correctly the snapshot that can cause
   1.209 -    ///either broken program, invalid state of the digraph, valid but
   1.210 -    ///not the restored digraph or no change. Because the runtime performance
   1.211 -    ///the validity of the snapshot is not stored.
   1.212 +    ///\note After a state is restored, you cannot restore a later state, 
   1.213 +    ///i.e. you cannot add the removed nodes and arcs again using
   1.214 +    ///another Snapshot instance.
   1.215 +    ///
   1.216 +    ///\warning Node splitting cannot be restored.
   1.217 +    ///\warning The validity of the snapshot is not stored due to
   1.218 +    ///performance reasons. If you do not use the snapshot correctly,
   1.219 +    ///it can cause broken program, invalid or not restored state of
   1.220 +    ///the digraph or no change.
   1.221      class Snapshot
   1.222      {
   1.223        SmartDigraph *_graph;
   1.224 @@ -357,39 +353,32 @@
   1.225        ///Default constructor.
   1.226  
   1.227        ///Default constructor.
   1.228 -      ///To actually make a snapshot you must call save().
   1.229 -      ///
   1.230 +      ///You have to call save() to actually make a snapshot.
   1.231        Snapshot() : _graph(0) {}
   1.232        ///Constructor that immediately makes a snapshot
   1.233  
   1.234 -      ///This constructor immediately makes a snapshot of the digraph.
   1.235 -      ///\param graph The digraph we make a snapshot of.
   1.236 -      Snapshot(SmartDigraph &graph) : _graph(&graph) {
   1.237 +      ///This constructor immediately makes a snapshot of the given digraph.
   1.238 +      ///
   1.239 +      Snapshot(SmartDigraph &gr) : _graph(&gr) {
   1.240          node_num=_graph->nodes.size();
   1.241          arc_num=_graph->arcs.size();
   1.242        }
   1.243  
   1.244        ///Make a snapshot.
   1.245  
   1.246 -      ///Make a snapshot of the digraph.
   1.247 -      ///
   1.248 -      ///This function can be called more than once. In case of a repeated
   1.249 +      ///This function makes a snapshot of the given digraph.
   1.250 +      ///It can be called more than once. In case of a repeated
   1.251        ///call, the previous snapshot gets lost.
   1.252 -      ///\param graph The digraph we make the snapshot of.
   1.253 -      void save(SmartDigraph &graph)
   1.254 -      {
   1.255 -        _graph=&graph;
   1.256 +      void save(SmartDigraph &gr) {
   1.257 +        _graph=&gr;
   1.258          node_num=_graph->nodes.size();
   1.259          arc_num=_graph->arcs.size();
   1.260        }
   1.261  
   1.262        ///Undo the changes until a snapshot.
   1.263  
   1.264 -      ///Undo the changes until a snapshot created by save().
   1.265 -      ///
   1.266 -      ///\note After you restored a state, you cannot restore
   1.267 -      ///a later state, in other word you cannot add again the arcs deleted
   1.268 -      ///by restore().
   1.269 +      ///This function undos the changes until the last snapshot
   1.270 +      ///created by save() or Snapshot(SmartDigraph&).
   1.271        void restore()
   1.272        {
   1.273          _graph->restoreSnapshot(*this);
   1.274 @@ -508,7 +497,7 @@
   1.275        node._id = nodes.size() - 1;
   1.276      }
   1.277  
   1.278 -    void next(Node& node) const {
   1.279 +    static void next(Node& node) {
   1.280        --node._id;
   1.281      }
   1.282  
   1.283 @@ -516,7 +505,7 @@
   1.284        arc._id = arcs.size() - 1;
   1.285      }
   1.286  
   1.287 -    void next(Arc& arc) const {
   1.288 +    static void next(Arc& arc) {
   1.289        --arc._id;
   1.290      }
   1.291  
   1.292 @@ -524,7 +513,7 @@
   1.293        arc._id = arcs.size() / 2 - 1;
   1.294      }
   1.295  
   1.296 -    void next(Edge& arc) const {
   1.297 +    static void next(Edge& arc) {
   1.298        --arc._id;
   1.299      }
   1.300  
   1.301 @@ -621,29 +610,26 @@
   1.302    ///
   1.303    /// \brief A smart undirected graph class.
   1.304    ///
   1.305 -  /// This is a simple and fast graph implementation.
   1.306 -  /// It is also quite memory efficient, but at the price
   1.307 -  /// that <b> it does support only limited (only stack-like)
   1.308 -  /// node and arc deletions</b>.
   1.309 -  /// It fully conforms to the \ref concepts::Graph "Graph concept".
   1.310 +  /// \ref SmartGraph is a simple and fast graph implementation.
   1.311 +  /// It is also quite memory efficient but at the price
   1.312 +  /// that it does not support node and edge deletion 
   1.313 +  /// (except for the Snapshot feature).
   1.314    ///
   1.315 -  /// \sa concepts::Graph.
   1.316 +  /// This type fully conforms to the \ref concepts::Graph "Graph concept"
   1.317 +  /// and it also provides some additional functionalities.
   1.318 +  /// Most of its member functions and nested classes are documented
   1.319 +  /// only in the concept class.
   1.320 +  ///
   1.321 +  /// \sa concepts::Graph
   1.322 +  /// \sa SmartDigraph
   1.323    class SmartGraph : public ExtendedSmartGraphBase {
   1.324      typedef ExtendedSmartGraphBase Parent;
   1.325  
   1.326    private:
   1.327 -
   1.328 -    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
   1.329 -
   1.330 -    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
   1.331 -    ///
   1.332 +    /// Graphs are \e not copy constructible. Use GraphCopy instead.
   1.333      SmartGraph(const SmartGraph &) : ExtendedSmartGraphBase() {};
   1.334 -
   1.335 -    ///\brief Assignment of SmartGraph to another one is \e not allowed.
   1.336 -    ///Use GraphCopy() instead.
   1.337 -
   1.338 -    ///Assignment of SmartGraph to another one is \e not allowed.
   1.339 -    ///Use GraphCopy() instead.
   1.340 +    /// \brief Assignment of a graph to another one is \e not allowed.
   1.341 +    /// Use GraphCopy instead.
   1.342      void operator=(const SmartGraph &) {}
   1.343  
   1.344    public:
   1.345 @@ -654,56 +640,77 @@
   1.346      ///
   1.347      SmartGraph() {}
   1.348  
   1.349 -    ///Add a new node to the graph.
   1.350 -
   1.351 -    /// Add a new node to the graph.
   1.352 +    /// \brief Add a new node to the graph.
   1.353 +    ///
   1.354 +    /// This function adds a new node to the graph.
   1.355      /// \return The new node.
   1.356      Node addNode() { return Parent::addNode(); }
   1.357  
   1.358 -    ///Add a new edge to the graph.
   1.359 -
   1.360 -    ///Add a new edge to the graph with node \c s
   1.361 -    ///and \c t.
   1.362 -    ///\return The new edge.
   1.363 -    Edge addEdge(const Node& s, const Node& t) {
   1.364 -      return Parent::addEdge(s, t);
   1.365 +    /// \brief Add a new edge to the graph.
   1.366 +    ///
   1.367 +    /// This function adds a new edge to the graph between nodes
   1.368 +    /// \c u and \c v with inherent orientation from node \c u to
   1.369 +    /// node \c v.
   1.370 +    /// \return The new edge.
   1.371 +    Edge addEdge(Node u, Node v) {
   1.372 +      return Parent::addEdge(u, v);
   1.373      }
   1.374  
   1.375      /// \brief Node validity check
   1.376      ///
   1.377 -    /// This function gives back true if the given node is valid,
   1.378 -    /// ie. it is a real node of the graph.
   1.379 +    /// This function gives back \c true if the given node is valid,
   1.380 +    /// i.e. it is a real node of the graph.
   1.381      ///
   1.382      /// \warning A removed node (using Snapshot) could become valid again
   1.383 -    /// when new nodes are added to the graph.
   1.384 +    /// if new nodes are added to the graph.
   1.385      bool valid(Node n) const { return Parent::valid(n); }
   1.386  
   1.387 +    /// \brief Edge validity check
   1.388 +    ///
   1.389 +    /// This function gives back \c true if the given edge is valid,
   1.390 +    /// i.e. it is a real edge of the graph.
   1.391 +    ///
   1.392 +    /// \warning A removed edge (using Snapshot) could become valid again
   1.393 +    /// if new edges are added to the graph.
   1.394 +    bool valid(Edge e) const { return Parent::valid(e); }
   1.395 +
   1.396      /// \brief Arc validity check
   1.397      ///
   1.398 -    /// This function gives back true if the given arc is valid,
   1.399 -    /// ie. it is a real arc of the graph.
   1.400 +    /// This function gives back \c true if the given arc is valid,
   1.401 +    /// i.e. it is a real arc of the graph.
   1.402      ///
   1.403      /// \warning A removed arc (using Snapshot) could become valid again
   1.404 -    /// when new edges are added to the graph.
   1.405 +    /// if new edges are added to the graph.
   1.406      bool valid(Arc a) const { return Parent::valid(a); }
   1.407  
   1.408 -    /// \brief Edge validity check
   1.409 -    ///
   1.410 -    /// This function gives back true if the given edge is valid,
   1.411 -    /// ie. it is a real edge of the graph.
   1.412 -    ///
   1.413 -    /// \warning A removed edge (using Snapshot) could become valid again
   1.414 -    /// when new edges are added to the graph.
   1.415 -    bool valid(Edge e) const { return Parent::valid(e); }
   1.416 -
   1.417      ///Clear the graph.
   1.418  
   1.419 -    ///Erase all the nodes and edges from the graph.
   1.420 +    ///This function erases all nodes and arcs from the graph.
   1.421      ///
   1.422      void clear() {
   1.423        Parent::clear();
   1.424      }
   1.425  
   1.426 +    /// Reserve memory for nodes.
   1.427 +
   1.428 +    /// Using this function, it is possible to avoid superfluous memory
   1.429 +    /// allocation: if you know that the graph you want to build will
   1.430 +    /// be large (e.g. it will contain millions of nodes and/or edges),
   1.431 +    /// then it is worth reserving space for this amount before starting
   1.432 +    /// to build the graph.
   1.433 +    /// \sa reserveEdge()
   1.434 +    void reserveNode(int n) { nodes.reserve(n); };
   1.435 +
   1.436 +    /// Reserve memory for edges.
   1.437 +
   1.438 +    /// Using this function, it is possible to avoid superfluous memory
   1.439 +    /// allocation: if you know that the graph you want to build will
   1.440 +    /// be large (e.g. it will contain millions of nodes and/or edges),
   1.441 +    /// then it is worth reserving space for this amount before starting
   1.442 +    /// to build the graph.
   1.443 +    /// \sa reserveNode()
   1.444 +    void reserveEdge(int m) { arcs.reserve(2 * m); };
   1.445 +
   1.446    public:
   1.447  
   1.448      class Snapshot;
   1.449 @@ -742,21 +749,22 @@
   1.450  
   1.451    public:
   1.452  
   1.453 -    ///Class to make a snapshot of the digraph and to restrore to it later.
   1.454 +    ///Class to make a snapshot of the graph and to restore it later.
   1.455  
   1.456 -    ///Class to make a snapshot of the digraph and to restrore to it later.
   1.457 +    ///Class to make a snapshot of the graph and to restore it later.
   1.458      ///
   1.459 -    ///The newly added nodes and arcs can be removed using the
   1.460 -    ///restore() function.
   1.461 +    ///The newly added nodes and edges can be removed using the
   1.462 +    ///restore() function. This is the only way for deleting nodes and/or
   1.463 +    ///edges from a SmartGraph structure.
   1.464      ///
   1.465 -    ///\note After you restore a state, you cannot restore
   1.466 -    ///a later state, in other word you cannot add again the arcs deleted
   1.467 -    ///by restore() using another one Snapshot instance.
   1.468 +    ///\note After a state is restored, you cannot restore a later state, 
   1.469 +    ///i.e. you cannot add the removed nodes and edges again using
   1.470 +    ///another Snapshot instance.
   1.471      ///
   1.472 -    ///\warning If you do not use correctly the snapshot that can cause
   1.473 -    ///either broken program, invalid state of the digraph, valid but
   1.474 -    ///not the restored digraph or no change. Because the runtime performance
   1.475 -    ///the validity of the snapshot is not stored.
   1.476 +    ///\warning The validity of the snapshot is not stored due to
   1.477 +    ///performance reasons. If you do not use the snapshot correctly,
   1.478 +    ///it can cause broken program, invalid or not restored state of
   1.479 +    ///the graph or no change.
   1.480      class Snapshot
   1.481      {
   1.482        SmartGraph *_graph;
   1.483 @@ -768,36 +776,30 @@
   1.484        ///Default constructor.
   1.485  
   1.486        ///Default constructor.
   1.487 -      ///To actually make a snapshot you must call save().
   1.488 -      ///
   1.489 +      ///You have to call save() to actually make a snapshot.
   1.490        Snapshot() : _graph(0) {}
   1.491        ///Constructor that immediately makes a snapshot
   1.492  
   1.493 -      ///This constructor immediately makes a snapshot of the digraph.
   1.494 -      ///\param graph The digraph we make a snapshot of.
   1.495 -      Snapshot(SmartGraph &graph) {
   1.496 -        graph.saveSnapshot(*this);
   1.497 +      /// This constructor immediately makes a snapshot of the given graph.
   1.498 +      ///
   1.499 +      Snapshot(SmartGraph &gr) {
   1.500 +        gr.saveSnapshot(*this);
   1.501        }
   1.502  
   1.503        ///Make a snapshot.
   1.504  
   1.505 -      ///Make a snapshot of the graph.
   1.506 -      ///
   1.507 -      ///This function can be called more than once. In case of a repeated
   1.508 +      ///This function makes a snapshot of the given graph.
   1.509 +      ///It can be called more than once. In case of a repeated
   1.510        ///call, the previous snapshot gets lost.
   1.511 -      ///\param graph The digraph we make the snapshot of.
   1.512 -      void save(SmartGraph &graph)
   1.513 +      void save(SmartGraph &gr)
   1.514        {
   1.515 -        graph.saveSnapshot(*this);
   1.516 +        gr.saveSnapshot(*this);
   1.517        }
   1.518  
   1.519 -      ///Undo the changes until a snapshot.
   1.520 +      ///Undo the changes until the last snapshot.
   1.521  
   1.522 -      ///Undo the changes until a snapshot created by save().
   1.523 -      ///
   1.524 -      ///\note After you restored a state, you cannot restore
   1.525 -      ///a later state, in other word you cannot add again the arcs deleted
   1.526 -      ///by restore().
   1.527 +      ///This function undos the changes until the last snapshot
   1.528 +      ///created by save() or Snapshot(SmartGraph&).
   1.529        void restore()
   1.530        {
   1.531          _graph->restoreSnapshot(*this);