RhodeCode

    public:

      /// The key type of the map.

      typedef K Key;    

      /// The value type of the map. (The type of objects associated with the keys).

      typedef T Value;

      /// Returns the value associated with a key.

      /// \bug Value shouldn't need to be default constructible.

      ///

      Value operator[](const Key &) const {return Value();}

      template<typename _ReadMap>

      struct Constraints {

	void constraints() {

	typename _WriteMap::Value own_val;

	Key& key;

	typename _WriteMap::Key& own_key;

	_WriteMap& m;

      };

    };

    /// Read/writable map concept.

    ///

    template<typename K, typename T>

    class ReadWriteMap : public ReadMap<K,T>,

			 public WriteMap<K,T>

    {

    public:

      };

    };

    /// Dereferable map concept

    /// Dereferable map concept.

    ///

    template<typename K, typename T, typename R, typename CR>

    class ReferenceMap : public ReadWriteMap<K,T>

    {

    public:

      /// Tag for reference maps.

      typedef True ReferenceMapTag;

      /// The key type of the map.

      typedef K Key;    

      typedef R Reference;

      /// The const reference type of the map.

      typedef CR ConstReference;

    protected:

      Value tmp;

    public:

      Reference operator[](const Key &) { return tmp; }

      ConstReference operator[](const Key &) const { return tmp; }

      /// Sets the value associated with a key.

      void set(const Key &k,const Value &t) { operator[](k)=t; }

      template<typename _ReferenceMap>

      struct ReferenceMapConcept {

	void constraints() {

	  checkConcept<ReadWriteMap, _ReferenceMap >();

	  m[key] = val;

	  val  = m[key];

	  m[key] = ref;