diff -r d8475431bbbb -r 8e85e6bbefdf lemon/maps.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lemon/maps.h	Mon May 23 04:48:14 2005 +0000
@@ -0,0 +1,841 @@
+/* -*- C++ -*-
+ * lemon/maps.h - Part of LEMON, a generic C++ optimization library
+ *
+ * Copyright (C) 2005 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_MAPS_H
+#define LEMON_MAPS_H
+
+#include <lemon/graph_utils.h>
+#include <lemon/utility.h>
+
+
+///\file
+///\ingroup maps
+///\brief Miscellaneous property maps
+///
+///\todo This file has the same name as the concept file in concept/,
+/// and this is not easily detectable in docs...
+
+#include <map>
+
+namespace lemon {
+
+  /// \addtogroup maps
+  /// @{
+
+  /// Base class of maps.
+
+  /// Base class of maps.
+  /// It provides the necessary <tt>typedef</tt>s required by the map concept.
+  template<typename K, typename T>
+  class MapBase
+  {
+  public:
+    ///\e
+    typedef K Key;
+    ///\e
+    typedef T Value;
+  };
+
+  /// Null map. (a.k.a. DoNothingMap)
+
+  /// If you have to provide a map only for its type definitions,
+  /// or if you have to provide a writable map, but
+  /// data written to it will sent to <tt>/dev/null</tt>...
+  template<typename K, typename T>
+  class NullMap : public MapBase<K,T>
+  {
+  public:
+    
+    typedef True NeedCopy;
+
+    /// Gives back a default constructed element.
+    T operator[](const K&) const { return T(); }
+    /// Absorbs the value.
+    void set(const K&, const T&) {}
+  };
+
+  template <typename K, typename V> 
+  NullMap<K, V> nullMap() {
+    return NullMap<K, V>();
+  }
+
+
+  /// Constant map.
+
+  /// This is a readable map which assigns a specified value to each key.
+  /// In other aspects it is equivalent to the \ref NullMap.
+  /// \todo set could be used to set the value.
+  template<typename K, typename T>
+  class ConstMap : public MapBase<K,T>
+  {
+    T v;
+  public:
+
+    typedef True NeedCopy;
+
+    /// Default constructor
+
+    /// The value of the map will be uninitialized. 
+    /// (More exactly it will be default constructed.)
+    ConstMap() {}
+    ///\e
+
+    /// \param _v The initial value of the map.
+    ///
+    ConstMap(const T &_v) : v(_v) {}
+
+    T operator[](const K&) const { return v; }
+    void set(const K&, const T&) {}
+
+    template<typename T1>
+    struct rebind {
+      typedef ConstMap<K,T1> other;
+    };
+
+    template<typename T1>
+    ConstMap(const ConstMap<K,T1> &, const T &_v) : v(_v) {}
+  };
+
+  ///Returns a \ref ConstMap class
+
+  ///This function just returns a \ref ConstMap class.
+  ///\relates ConstMap
+  template<class V,class K> 
+  inline ConstMap<V,K> constMap(const K &k) 
+  {
+    return ConstMap<V,K>(k);
+  }
+
+
+  //to document later
+  template<typename T, T v>
+  struct Const { };
+  //to document later
+  template<typename K, typename V, V v>
+  class ConstMap<K, Const<V, v> > : public MapBase<K, V>
+  {
+  public:
+    ConstMap() { }
+    V operator[](const K&) const { return v; }
+    void set(const K&, const V&) { }
+  };
+
+  /// \c std::map wrapper
+
+  /// This is essentially a wrapper for \c std::map. With addition that
+  /// you can specify a default value different from \c Value() .
+  ///
+  /// \todo Provide allocator parameter...
+  template <typename K, typename T, typename Compare = std::less<K> >
+  class StdMap : public std::map<K,T,Compare> {
+    typedef std::map<K,T,Compare> parent;
+    T v;
+    typedef typename parent::value_type PairType;
+
+  public:
+    typedef K Key;
+    typedef T Value;
+    typedef T& Reference;
+    typedef const T& ConstReference;
+
+
+    StdMap() : v() {}
+    /// Constructor with specified default value
+    StdMap(const T& _v) : v(_v) {}
+
+    /// \brief Constructs the map from an appropriate std::map.
+    ///
+    /// \warning Inefficient: copies the content of \c m !
+    StdMap(const parent &m) : parent(m) {}
+    /// \brief Constructs the map from an appropriate std::map, and explicitly
+    /// specifies a default value.
+    ///
+    /// \warning Inefficient: copies the content of \c m !
+    StdMap(const parent &m, const T& _v) : parent(m), v(_v) {}
+    
+    template<typename T1, typename Comp1>
+    StdMap(const StdMap<Key,T1,Comp1> &m, const T &_v) { 
+      //FIXME; 
+    }
+
+    Reference operator[](const Key &k) {
+      return insert(PairType(k,v)).first -> second;
+    }
+    ConstReference operator[](const Key &k) const {
+      typename parent::iterator i = lower_bound(k);
+      if (i == parent::end() || parent::key_comp()(k, (*i).first))
+	return v;
+      return (*i).second;
+    }
+    void set(const Key &k, const T &t) {
+      parent::operator[](k) = t;
+    }
+
+    /// Changes the default value of the map.
+    /// \return Returns the previous default value.
+    ///
+    /// \warning The value of some keys (which has already been queried, but
+    /// the value has been unchanged from the default) may change!
+    T setDefault(const T &_v) { T old=v; v=_v; return old; }
+
+    template<typename T1>
+    struct rebind {
+      typedef StdMap<Key,T1,Compare> other;
+    };
+  };
+
+  /// @}
+
+  /// \addtogroup map_adaptors
+  /// @{
+
+
+  ///Convert the \c Value of a maps to another type.
+
+  ///This \ref concept::ReadMap "read only map"
+  ///converts the \c Value of a maps to type \c T.
+  ///Its \c Value is inherited from \c M.
+  ///
+  ///Actually,
+  ///\code
+  ///  ConvertMap<X> sh(x,v);
+  ///\endcode
+  ///it is equivalent with
+  ///\code
+  ///  ConstMap<X::Key, X::Value> c_tmp(v);
+  ///  AddMap<X, ConstMap<X::Key, X::Value> > sh(x,v);
+  ///\endcode
+  ///\bug wrong documentation
+  template<class M, class T> 
+  class ConvertMap {
+    typename SmartConstReference<M>::Type m;
+  public:
+
+    typedef True NeedCopy;
+
+    typedef typename M::Key Key;
+    typedef T Value;
+
+    ///Constructor
+
+    ///Constructor
+    ///\param _m is the undelying map
+    ///\param _v is the convert value
+    ConvertMap(const M &_m) : m(_m) {};
+
+    /// \brief The subscript operator.
+    ///
+    /// The subscript operator.
+    /// \param edge The edge 
+    /// \return The target of the edge 
+    Value operator[](Key k) const {return m[k];}
+  };
+  
+  ///Returns an \ref ConvertMap class
+
+  ///This function just returns an \ref ConvertMap class.
+  ///\relates ConvertMap
+  ///\todo The order of the template parameters are changed.
+  template<class T, class M>
+  inline ConvertMap<M,T> convertMap(const M &m) 
+  {
+    return ConvertMap<M,T>(m);
+  }
+
+  ///Sum of two maps
+
+  ///This \ref concept::ReadMap "read only map" returns the sum of the two
+  ///given maps. Its \c Key and \c Value will be inherited from \c M1.
+  ///The \c Key and \c Value of M2 must be convertible to those of \c M1.
+
+  template<class M1,class M2> 
+  class AddMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+
+  public:
+
+    typedef True NeedCopy;
+
+    typedef typename M1::Key Key;
+    typedef typename M1::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    AddMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};
+    Value operator[](Key k) const {return m1[k]+m2[k];}
+  };
+  
+  ///Returns an \ref AddMap class
+
+  ///This function just returns an \ref AddMap class.
+  ///\todo How to call these type of functions?
+  ///
+  ///\relates AddMap
+  ///\todo Wrong scope in Doxygen when \c \\relates is used
+  template<class M1,class M2> 
+  inline AddMap<M1,M2> addMap(const M1 &m1,const M2 &m2) 
+  {
+    return AddMap<M1,M2>(m1,m2);
+  }
+
+  ///Shift a maps with a constant.
+
+  ///This \ref concept::ReadMap "read only map" returns the sum of the
+  ///given map and a constant value.
+  ///Its \c Key and \c Value is inherited from \c M.
+  ///
+  ///Actually,
+  ///\code
+  ///  ShiftMap<X> sh(x,v);
+  ///\endcode
+  ///it is equivalent with
+  ///\code
+  ///  ConstMap<X::Key, X::Value> c_tmp(v);
+  ///  AddMap<X, ConstMap<X::Key, X::Value> > sh(x,v);
+  ///\endcode
+  template<class M> 
+  class ShiftMap
+  {
+    typename SmartConstReference<M>::Type m;
+    typename M::Value v;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M::Key Key;
+    typedef typename M::Value Value;
+
+    ///Constructor
+
+    ///Constructor
+    ///\param _m is the undelying map
+    ///\param _v is the shift value
+    ShiftMap(const M &_m,const Value &_v ) : m(_m), v(_v) {};
+    Value operator[](Key k) const {return m[k]+v;}
+  };
+  
+  ///Returns an \ref ShiftMap class
+
+  ///This function just returns an \ref ShiftMap class.
+  ///\relates ShiftMap
+  ///\todo A better name is required.
+  template<class M> 
+  inline ShiftMap<M> shiftMap(const M &m,const typename M::Value &v) 
+  {
+    return ShiftMap<M>(m,v);
+  }
+
+  ///Difference of two maps
+
+  ///This \ref concept::ReadMap "read only map" returns the difference
+  ///of the values returned by the two
+  ///given maps. Its \c Key and \c Value will be inherited from \c M1.
+  ///The \c Key and \c Value of \c M2 must be convertible to those of \c M1.
+
+  template<class M1,class M2> 
+  class SubMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M1::Key Key;
+    typedef typename M1::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    SubMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};
+    Value operator[](Key k) const {return m1[k]-m2[k];}
+  };
+  
+  ///Returns a \ref SubMap class
+
+  ///This function just returns a \ref SubMap class.
+  ///
+  ///\relates SubMap
+  template<class M1,class M2> 
+  inline SubMap<M1,M2> subMap(const M1 &m1,const M2 &m2) 
+  {
+    return SubMap<M1,M2>(m1,m2);
+  }
+
+  ///Product of two maps
+
+  ///This \ref concept::ReadMap "read only map" returns the product of the
+  ///values returned by the two
+  ///given
+  ///maps. Its \c Key and \c Value will be inherited from \c M1.
+  ///The \c Key and \c Value of \c M2 must be convertible to those of \c M1.
+
+  template<class M1,class M2> 
+  class MulMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M1::Key Key;
+    typedef typename M1::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    MulMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};
+    Value operator[](Key k) const {return m1[k]*m2[k];}
+  };
+  
+  ///Returns a \ref MulMap class
+
+  ///This function just returns a \ref MulMap class.
+  ///\relates MulMap
+  template<class M1,class M2> 
+  inline MulMap<M1,M2> mulMap(const M1 &m1,const M2 &m2) 
+  {
+    return MulMap<M1,M2>(m1,m2);
+  }
+ 
+  ///Scale a maps with a constant.
+
+  ///This \ref concept::ReadMap "read only map" returns the value of the
+  ///given map multipied with a constant value.
+  ///Its \c Key and \c Value is inherited from \c M.
+  ///
+  ///Actually,
+  ///\code
+  ///  ScaleMap<X> sc(x,v);
+  ///\endcode
+  ///it is equivalent with
+  ///\code
+  ///  ConstMap<X::Key, X::Value> c_tmp(v);
+  ///  MulMap<X, ConstMap<X::Key, X::Value> > sc(x,v);
+  ///\endcode
+  template<class M> 
+  class ScaleMap
+  {
+    typename SmartConstReference<M>::Type m;
+    typename M::Value v;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M::Key Key;
+    typedef typename M::Value Value;
+
+    ///Constructor
+
+    ///Constructor
+    ///\param _m is the undelying map
+    ///\param _v is the scaling value
+    ScaleMap(const M &_m,const Value &_v ) : m(_m), v(_v) {};
+    Value operator[](Key k) const {return m[k]*v;}
+  };
+  
+  ///Returns an \ref ScaleMap class
+
+  ///This function just returns an \ref ScaleMap class.
+  ///\relates ScaleMap
+  ///\todo A better name is required.
+  template<class M> 
+  inline ScaleMap<M> scaleMap(const M &m,const typename M::Value &v) 
+  {
+    return ScaleMap<M>(m,v);
+  }
+
+  ///Quotient of two maps
+
+  ///This \ref concept::ReadMap "read only map" returns the quotient of the
+  ///values returned by the two
+  ///given maps. Its \c Key and \c Value will be inherited from \c M1.
+  ///The \c Key and \c Value of \c M2 must be convertible to those of \c M1.
+
+  template<class M1,class M2> 
+  class DivMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M1::Key Key;
+    typedef typename M1::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    DivMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};
+    Value operator[](Key k) const {return m1[k]/m2[k];}
+  };
+  
+  ///Returns a \ref DivMap class
+
+  ///This function just returns a \ref DivMap class.
+  ///\relates DivMap
+  template<class M1,class M2> 
+  inline DivMap<M1,M2> divMap(const M1 &m1,const M2 &m2) 
+  {
+    return DivMap<M1,M2>(m1,m2);
+  }
+  
+  ///Composition of two maps
+
+  ///This \ref concept::ReadMap "read only map" returns the composition of
+  ///two
+  ///given maps. That is to say, if \c m1 is of type \c M1 and \c m2 is
+  ///of \c M2,
+  ///then for
+  ///\code
+  ///  ComposeMap<M1,M2> cm(m1,m2);
+  ///\endcode
+  /// <tt>cm[x]</tt> will be equal to <tt>m1[m2[x]]</tt>
+  ///
+  ///Its \c Key is inherited from \c M2 and its \c Value is from
+  ///\c M1.
+  ///The \c M2::Value must be convertible to \c M1::Key.
+  ///\todo Check the requirements.
+
+  template<class M1,class M2> 
+  class ComposeMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M2::Key Key;
+    typedef typename M1::Value Value;
+
+    typedef True NeedCopy;
+
+    ///Constructor
+
+    ///\e
+    ///
+    ComposeMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};
+    Value operator[](Key k) const {return m1[m2[k]];}
+  };
+  ///Returns a \ref ComposeMap class
+
+  ///This function just returns a \ref ComposeMap class.
+  ///
+  ///\relates ComposeMap
+  template<class M1,class M2> 
+  inline ComposeMap<M1,M2> composeMap(const M1 &m1,const M2 &m2) 
+  {
+    return ComposeMap<M1,M2>(m1,m2);
+  }
+  
+  ///Combine of two maps using an STL (binary) functor.
+
+  ///Combine of two maps using an STL (binary) functor.
+  ///
+  ///
+  ///This \ref concept::ReadMap "read only map" takes to maps and a
+  ///binary functor and returns the composition of
+  ///two
+  ///given maps unsing the functor. 
+  ///That is to say, if \c m1 and \c m2 is of type \c M1 and \c M2
+  ///and \c f is of \c F,
+  ///then for
+  ///\code
+  ///  CombineMap<M1,M2,F,V> cm(m1,m2,f);
+  ///\endcode
+  /// <tt>cm[x]</tt> will be equal to <tt>f(m1[x],m2[x])</tt>
+  ///
+  ///Its \c Key is inherited from \c M1 and its \c Value is \c V.
+  ///The \c M2::Value and \c M1::Value must be convertible to the corresponding
+  ///input parameter of \c F and the return type of \c F must be convertible
+  ///to \c V.
+  ///\todo Check the requirements.
+
+  template<class M1,class M2,class F,class V = typename F::result_type> 
+  class CombineMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+    F f;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M1::Key Key;
+    typedef V Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    CombineMap(const M1 &_m1,const M2 &_m2,const F &_f)
+      : m1(_m1), m2(_m2), f(_f) {};
+    Value operator[](Key k) const {return f(m1[k],m2[k]);}
+  };
+  
+  ///Returns a \ref CombineMap class
+
+  ///This function just returns a \ref CombineMap class.
+  ///
+  ///Only the first template parameter (the value type) must be given.
+  ///
+  ///For example if \c m1 and \c m2 are both \c double valued maps, then 
+  ///\code
+  ///combineMap<double>(m1,m2,std::plus<double>)
+  ///\endcode
+  ///is equivalent with
+  ///\code
+  ///addMap(m1,m2)
+  ///\endcode
+  ///
+  ///\relates CombineMap
+  template<class M1,class M2,class F> 
+  inline CombineMap<M1,M2,F> combineMap(const M1 &m1,const M2 &m2,const F &f) 
+  {
+    return CombineMap<M1,M2,F>(m1,m2,f);
+  }
+
+  ///Negative value of a map
+
+  ///This \ref concept::ReadMap "read only map" returns the negative
+  ///value of the
+  ///value returned by the
+  ///given map. Its \c Key and \c Value will be inherited from \c M.
+  ///The unary \c - operator must be defined for \c Value, of course.
+
+  template<class M> 
+  class NegMap
+  {
+    typename SmartConstReference<M>::Type m;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M::Key Key;
+    typedef typename M::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    NegMap(const M &_m) : m(_m) {};
+    Value operator[](Key k) const {return -m[k];}
+  };
+  
+  ///Returns a \ref NegMap class
+
+  ///This function just returns a \ref NegMap class.
+  ///\relates NegMap
+  template<class M> 
+  inline NegMap<M> negMap(const M &m) 
+  {
+    return NegMap<M>(m);
+  }
+
+
+  ///Absolute value of a map
+
+  ///This \ref concept::ReadMap "read only map" returns the absolute value
+  ///of the
+  ///value returned by the
+  ///given map. Its \c Key and \c Value will be inherited
+  ///from <tt>M</tt>. <tt>Value</tt>
+  ///must be comparable to <tt>0</tt> and the unary <tt>-</tt>
+  ///operator must be defined for it, of course.
+  ///
+  ///\bug We need a unified way to handle the situation below:
+  ///\code
+  ///  struct _UnConvertible {};
+  ///  template<class A> inline A t_abs(A a) {return _UnConvertible();}
+  ///  template<> inline int t_abs<>(int n) {return abs(n);}
+  ///  template<> inline long int t_abs<>(long int n) {return labs(n);}
+  ///  template<> inline long long int t_abs<>(long long int n) {return ::llabs(n);}
+  ///  template<> inline float t_abs<>(float n) {return fabsf(n);}
+  ///  template<> inline double t_abs<>(double n) {return fabs(n);}
+  ///  template<> inline long double t_abs<>(long double n) {return fabsl(n);}
+  ///\endcode
+  
+
+  template<class M> 
+  class AbsMap
+  {
+    typename SmartConstReference<M>::Type m;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M::Key Key;
+    typedef typename M::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    AbsMap(const M &_m) : m(_m) {};
+    Value operator[](Key k) const {Value tmp=m[k]; return tmp>=0?tmp:-tmp;}
+  };
+  
+  ///Returns a \ref AbsMap class
+
+  ///This function just returns a \ref AbsMap class.
+  ///\relates AbsMap
+  template<class M> 
+  inline AbsMap<M> absMap(const M &m) 
+  {
+    return AbsMap<M>(m);
+  }
+
+  ///Converts an STL style functor to a map
+
+  ///This \ref concept::ReadMap "read only map" returns the value
+  ///of a
+  ///given map.
+  ///
+  ///Template parameters \c K and \c V will become its
+  ///\c Key and \c Value. They must be given explicitely
+  ///because a functor does not provide such typedefs.
+  ///
+  ///Parameter \c F is the type of the used functor.
+  
+
+  template<class K,class V,class F> 
+  class FunctorMap
+  {
+    const F &f;
+  public:
+
+    typedef True NeedCopy;
+    typedef K Key;
+    typedef V Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    FunctorMap(const F &_f) : f(_f) {};
+    Value operator[](Key k) const {return f(k);}
+  };
+  
+  ///Returns a \ref FunctorMap class
+
+  ///This function just returns a \ref FunctorMap class.
+  ///
+  ///The third template parameter isn't necessary to be given.
+  ///\relates FunctorMap
+  template<class K,class V, class F>
+  inline FunctorMap<K,V,F> functorMap(const F &f) 
+  {
+    return FunctorMap<K,V,F>(f);
+  }
+
+  ///Converts a map to an STL style (unary) functor
+
+  ///This class Converts a map to an STL style (unary) functor.
+  ///that is it provides an <tt>operator()</tt> to read its values.
+  ///
+  ///For the sake of convenience it also works as
+  ///a ususal \ref concept::ReadMap "readable map", i.e
+  ///<tt>operator[]</tt> and the \c Key and \c Value typedefs also exist.
+
+  template<class M> 
+  class MapFunctor
+  {
+    typename SmartConstReference<M>::Type m;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M::Key argument_type;
+    typedef typename M::Value result_type;
+    typedef typename M::Key Key;
+    typedef typename M::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    MapFunctor(const M &_m) : m(_m) {};
+    ///Returns a value of the map
+    
+    ///\e
+    ///
+    Value operator()(Key k) const {return m[k];}
+    ///\e
+    ///
+    Value operator[](Key k) const {return m[k];}
+  };
+  
+  ///Returns a \ref MapFunctor class
+
+  ///This function just returns a \ref MapFunctor class.
+  ///\relates MapFunctor
+  template<class M> 
+  inline MapFunctor<M> mapFunctor(const M &m) 
+  {
+    return MapFunctor<M>(m);
+  }
+
+
+  ///Apply all map setting operations to two maps
+
+  ///This map has two \ref concept::WriteMap "writable map"
+  ///parameters and each write request will be passed to both of them.
+  ///If \c M1 is also \ref concept::ReadMap "readable",
+  ///then the read operations will return the
+  ///corresponding values of \c M1.
+  ///
+  ///The \c Key and \c Value will be inherited from \c M1.
+  ///The \c Key and \c Value of M2 must be convertible from those of \c M1.
+
+  template<class M1,class M2> 
+  class ForkMap
+  {
+    typename SmartConstReference<M1>::Type m1;
+    typename SmartConstReference<M2>::Type m2;
+  public:
+
+    typedef True NeedCopy;
+    typedef typename M1::Key Key;
+    typedef typename M1::Value Value;
+
+    ///Constructor
+
+    ///\e
+    ///
+    ForkMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};
+    Value operator[](Key k) const {return m1[k];}
+    void set(Key k,const Value &v) {m1.set(k,v); m2.set(k,v);}
+  };
+  
+  ///Returns an \ref ForkMap class
+
+  ///This function just returns an \ref ForkMap class.
+  ///\todo How to call these type of functions?
+  ///
+  ///\relates ForkMap
+  ///\todo Wrong scope in Doxygen when \c \\relates is used
+  template<class M1,class M2> 
+  inline ForkMap<M1,M2> forkMap(const M1 &m1,const M2 &m2) 
+  {
+    return ForkMap<M1,M2>(m1,m2);
+  }
+
+  /// @}
+  
+}
+
+
+#endif // LEMON_MAPS_H