/* -*- 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/utility.h>

#include <lemon/traits.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 MapBase<K, T> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    /// 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> {

  private:

    T v;

  public:

    typedef MapBase<K, T> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    /// 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<typename K, typename V> 

  inline ConstMap<K, V> constMap(const V &v) {

    return ConstMap<K, V>(v);

  }

  //\todo to document later

  template<typename T, T v>

  struct Const { };

  //\todo to document later

  template<typename K, typename V, V v>

  class ConstMap<K, Const<V, v> > : public MapBase<K, V> {

  public:

    typedef MapBase<K, V> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ConstMap() { }

    V operator[](const K&) const { return v; }

    void set(const K&, const V&) { }

  };

  ///Returns a \ref ConstMap class

  ///This function just returns a \ref ConstMap class.

  ///\relates ConstMap

  template<typename K, typename V, V v> 

  inline ConstMap<K, Const<V, v> > constMap() {

    return ConstMap<K, Const<V, 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:

    ///\e

    typedef K Key;

    ///\e

    typedef T Value;

    ///\e

    typedef T& Reference;

    ///\e

    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

  /// @{

  /// \brief Identity mapping.

  ///

  /// This mapping gives back the given key as value without any

  /// modification. 

  template <typename T>

  class IdentityMap : public MapBase<T, T> {

  public:

    typedef MapBase<T, T> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    const T& operator[](const T& t) const {

      return t;

    }

  };

  ///Returns an \ref IdentityMap class

  ///This function just returns an \ref IdentityMap class.

  ///\relates IdentityMap

  template<typename T>

  inline IdentityMap<T> identityMap() {

    return IdentityMap<T>();

  }

  ///Convert the \c Value of a map to another type.

  ///This \ref concept::ReadMap "read only map"

  ///converts the \c Value of a maps to type \c T.

  ///Its \c Key is inherited from \c M.

  template <typename M, typename T> 

  class ConvertMap : public MapBase<typename M::Key, T> {

    const M& m;

  public:

    typedef MapBase<typename M::Key, T> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    ///Constructor

    ///\param _m is the underlying map

    ConvertMap(const M &_m) : m(_m) {};

    /// \brief The subscript operator.

    ///

    /// The subscript operator.

    /// \param k The key

    /// \return The target of the edge 

    Value operator[](const 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<typename T, typename 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<typename M1, typename M2> 

  class AddMap : public MapBase<typename M1::Key, typename M1::Value> {

    const M1& m1;

    const M2& m2;

  public:

    typedef MapBase<typename M1::Key, typename M1::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename M1, typename M2> 

  inline AddMap<M1, M2> addMap(const M1 &m1,const M2 &m2) {

    return AddMap<M1, M2>(m1,m2);

  }

  ///Shift a map 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

  ///is equivalent with

  ///\code

  ///  ConstMap<X::Key, X::Value> c_tmp(v);

  ///  AddMap<X, ConstMap<X::Key, X::Value> > sh(x,v);

  ///\endcode

  template<typename M, typename C = typename M::Value> 

  class ShiftMap : public MapBase<typename M::Key, typename M::Value> {

    const M& m;

    C v;

  public:

    typedef MapBase<typename M::Key, typename M::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    ///Constructor

    ///\param _m is the undelying map

    ///\param _v is the shift value

    ShiftMap(const M &_m, const C &_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<typename M, typename C> 

  inline ShiftMap<M, C> shiftMap(const M &m,const C &v) {

    return ShiftMap<M, C>(m,v);

  }

  ///Difference of two maps

  ///This \ref concept::ReadMap "read only map" returns the difference

  ///of the values of 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<typename M1, typename M2> 

  class SubMap : public MapBase<typename M1::Key, typename M1::Value> {

    const M1& m1;

    const M2& m2;

  public:

    typedef MapBase<typename M1::Key, typename M1::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename M1, typename 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 of 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<typename M1, typename M2> 

  class MulMap : public MapBase<typename M1::Key, typename M1::Value> {

    const M1& m1;

    const M2& m2;

  public:

    typedef MapBase<typename M1::Key, typename M1::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename M1, typename M2> 

  inline MulMap<M1, M2> mulMap(const M1 &m1,const M2 &m2) {

    return MulMap<M1, M2>(m1,m2);

  }

  ///Scales a maps with a constant.

  ///This \ref concept::ReadMap "read only map" returns the value of the

  ///given map multiplied from the left side with a constant value.

  ///Its \c Key and \c Value is inherited from \c M.

  ///

  ///Actually,

  ///\code

  ///  ScaleMap<X> sc(x,v);

  ///\endcode

  ///is equivalent with

  ///\code

  ///  ConstMap<X::Key, X::Value> c_tmp(v);

  ///  MulMap<X, ConstMap<X::Key, X::Value> > sc(x,v);

  ///\endcode

  template<typename M, typename C = typename M::Value> 

  class ScaleMap : public MapBase<typename M::Key, typename M::Value> {

    const M& m;

    C v;

  public:

    typedef MapBase<typename M::Key, typename M::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    ///Constructor

    ///\param _m is the undelying map

    ///\param _v is the scaling value

    ScaleMap(const M &_m, const C &_v ) : m(_m), v(_v) {};

    Value operator[](Key k) const {return v * m[k];}

  };

  ///Returns an \ref ScaleMap class

  ///This function just returns an \ref ScaleMap class.

  ///\relates ScaleMap

  ///\todo A better name is required.

  template<typename M, typename C> 

  inline ScaleMap<M, C> scaleMap(const M &m,const C &v) {

    return ScaleMap<M, C>(m,v);

  }

  ///Quotient of two maps

  ///This \ref concept::ReadMap "read only map" returns the quotient of the

  ///values of 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<typename M1, typename M2> 

  class DivMap : public MapBase<typename M1::Key, typename M1::Value> {

    const M1& m1;

    const M2& m2;

  public:

    typedef MapBase<typename M1::Key, typename M1::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename M1, typename 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 <typename M1, typename M2> 

  class ComposeMap : public MapBase<typename M2::Key, typename M1::Value> {

    const M1& m1;

    const M2& m2;

  public:

    typedef MapBase<typename M2::Key, typename M1::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    ComposeMap(const M1 &_m1,const M2 &_m2) : m1(_m1), m2(_m2) {};

    typename MapTraits<M1>::ConstReturnValue

    operator[](Key k) const {return m1[m2[k]];}

  };

  ///Returns a \ref ComposeMap class

  ///This function just returns a \ref ComposeMap class.

  ///

  ///\relates ComposeMap

  template <typename M1, typename M2> 

  inline ComposeMap<M1, M2> composeMap(const M1 &m1,const M2 &m2) {

    return ComposeMap<M1, M2>(m1,m2);

  }

  ///Combines of two maps using an STL (binary) functor.

  ///Combines of two maps using an STL (binary) functor.

  ///

  ///

  ///This \ref concept::ReadMap "read only map" takes two maps and a

  ///binary functor and returns the composition of

  ///the 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<typename M1, typename M2, typename F,

	   typename V = typename F::result_type,

	   typename NC = False> 

  class CombineMap : public MapBase<typename M1::Key, V> {

    const M1& m1;

    const M2& m2;

    F f;

  public:

    typedef MapBase<typename M1::Key, V> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename M1, typename M2, typename F, typename V> 

  inline CombineMap<M1, M2, F, V> 

  combineMap(const M1& m1,const M2& m2, const F& f) {

    return CombineMap<M1, M2, F, V>(m1,m2,f);

  }

  template<typename M1, typename M2, typename F> 

  inline CombineMap<M1, M2, F, typename F::result_type> 

  combineMap(const M1& m1, const M2& m2, const F& f) {

    return combineMap<M1, M2, F, typename F::result_type>(m1,m2,f);

  }

  template<typename M1, typename M2, typename K1, typename K2, typename V> 

  inline CombineMap<M1, M2, V (*)(K1, K2), V> 

  combineMap(const M1 &m1, const M2 &m2, V (*f)(K1, K2)) {

    return combineMap<M1, M2, V (*)(K1, K2), V>(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<typename M> 

  class NegMap : public MapBase<typename M::Key, typename M::Value> {

    const M& m;

  public:

    typedef MapBase<typename M::Key, typename M::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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 <typename 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<typename M> 

  class AbsMap : public MapBase<typename M::Key, typename M::Value> {

    const M& m;

  public:

    typedef MapBase<typename M::Key, typename M::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename 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<typename F, 

	   typename K = typename F::argument_type, 

	   typename V = typename F::result_type,

	   typename NC = False> 

  class FunctorMap : public MapBase<K, V> {

    F f;

  public:

    typedef MapBase<K, V> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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<typename K, typename V, typename F> inline 

  FunctorMap<F, K, V> functorMap(const F &f) {

    return FunctorMap<F, K, V>(f);

  }

  template <typename F> inline 

  FunctorMap<F, typename F::argument_type, typename F::result_type> 

  functorMap(const F &f) {

    return FunctorMap<F, typename F::argument_type, 

      typename F::result_type>(f);

  }

  template <typename K, typename V> inline 

  FunctorMap<V (*)(K), K, V> functorMap(V (*f)(K)) {

    return FunctorMap<V (*)(K), K, V>(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 <typename M> 

  class MapFunctor : public MapBase<typename M::Key, typename M::Value> {

    const M& m;

  public:

    typedef MapBase<typename M::Key, typename M::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///\e

    typedef typename M::Key argument_type;

    ///\e

    typedef typename M::Value result_type;

    ///Constructor

    MapFunctor(const M &_m) : m(_m) {};

    ///Returns a value of the map

    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<typename M> 

  inline MapFunctor<M> mapFunctor(const M &m) {

    return MapFunctor<M>(m);

  }

  ///Applies 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<typename  M1, typename M2> 

  class ForkMap : public MapBase<typename M1::Key, typename M1::Value> {

    const M1& m1;

    const M2& m2;

  public:

    typedef MapBase<typename M1::Key, typename M1::Value> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    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 <typename M1, typename M2> 

  inline ForkMap<M1, M2> forkMap(const M1 &m1,const M2 &m2) {

    return ForkMap<M1, M2>(m1,m2);

  }

  /* ************* BOOL MAPS ******************* */

  ///Logical 'not' of a map

  ///This bool \ref concept::ReadMap "read only map" returns the 

  ///logical negation of

  ///value returned by the

  ///given map. Its \c Key and will be inherited from \c M,

  ///its Value is <tt>bool</tt>.

  template <typename M> 

  class NotMap : public MapBase<typename M::Key, bool> {

    const M& m;

  public:

    typedef MapBase<typename M::Key, bool> Parent;

    typedef typename Parent::Key Key;

    typedef typename Parent::Value Value;

    ///Constructor

    NotMap(const M &_m) : m(_m) {};

    Value operator[](Key k) const {return !m[k];}

  };

  ///Returns a \ref NotMap class

  ///This function just returns a \ref NotMap class.

  ///\relates NotMap

  template <typename M> 

  inline NotMap<M> notMap(const M &m) {

    return NotMap<M>(m);

  }

  /// @}

}

#endif // LEMON_MAPS_H