Encapsulating containers like map and set with a single Red-Black Tree (RBTree) template presents several design considerations. The key goals include implementing iterators, supporting increment/decrement operations, and enforcing container-specific constraints: preventing value modification in set and key modification in map.

Adapting a Single Tree Structure

A unified RBTree template must handle differing data requirements:

• For map, data is a pair<const K, V>. The const K ensures the key is immutable.
• For set, the key and data type are identical (K). The template parameters K and T both become K.

A functor KeyOfT extracts the comparison key from the stored data. For map, it returns the first member of the pair; for set, it returns the value itself.

The Insert method returns a pair<Node*, bool>. Using a raw node pointer resolves potential type conflicts when the same RBTree must return different iterator types (iterator vs const_iterator) to its encapsulating containers.

Red-Black Tree Iterator

The iterator provides access to nodes in sorted order. The core structure includes dereferencing operators and comparison logic.

template<typename DataType>
struct TreeIterator {
    typedef RBTreeNode<DataType> TreeNode;
    typedef TreeIterator<DataType> IteratorSelf;
    TreeNode* nodePtr;

    TreeIterator(TreeNode* node) : nodePtr(node) {}

    DataType& operator*() { return nodePtr->nodeData; }
    DataType* operator->() { return &(nodePtr->nodeData); }

    bool operator!=(const IteratorSelf& other) const {
        return nodePtr != other.nodePtr;
    }
    bool operator==(const IteratorSelf& other) const {
        return nodePtr == other.nodePtr;
    }

Implementing Pre-increment (++)

The iterator advances to the next node in an in-order traversal.

• If the current node has a right child, the successor is the leftmost node in that right subtree.
• Otherwise, traverse upwards until reaching an ancestor where the current node is in the ancestor's left subtree. That ancestor is the successor.

    IteratorSelf& operator++() {
        if (nodePtr->rightChild) {
            TreeNode* temp = nodePtr->rightChild;
            while (temp->leftChild) {
                temp = temp->leftChild;
            }
            nodePtr = temp;
        } else {
            TreeNode* curr = nodePtr;
            TreeNode* parent = curr->parentNode;
            while (parent && curr == parent->rightChild) {
                curr = parent;
                parent = parent->parentNode;
            }
            nodePtr = parent;
        }
        return *this;
    }
};

RBTree Public Interface

template<typename KeyType, typename DataType, typename KeyExtractor>
class RedBlackTree {
    typedef RBTreeNode<DataType> TreeNode;
public:
    typedef TreeIterator<DataType> iterator;

    iterator begin() {
        TreeNode* temp = rootNode;
        while (temp && temp->leftChild) {
            temp = temp->leftChild;
        }
        return iterator(temp);
    }

    iterator end() {
        return iterator(nullptr);
    }

    std::pair<TreeNode*, bool> Insert(const DataType& data) {
        // ... Insertion and balancing logic ...
        return std::make_pair(newNode, insertionSuccess);
    }
private:
    TreeNode* rootNode = nullptr;
};

Map Implementation

namespace ContainerLib {
    template<typename Key, typename Value>
    class Map {
        struct MapKeyExtractor {
            const Key& operator()(const std::pair<Key, Value>& element) const {
                return element.first;
            }
        };
        RedBlackTree<Key, std::pair<const Key, Value>, MapKeyExtractor> rbTree;
    public:
        typedef typename decltype(rbTree)::iterator iterator;

        iterator begin() { return rbTree.begin(); }
        iterator end() { return rbTree.end(); }

        std::pair<iterator, bool> insert(const std::pair<Key, Value>& element) {
            return rbTree.Insert(element);
        }

        Value& operator[](const Key& k) {
            auto result = insert({k, Value{}});
            return (result.first)->second;
        }
    };
}

Set Implementation

namespace ContainerLib {
    template<typename Key>
    class Set {
        struct SetKeyExtractor {
            const Key& operator()(const Key& element) const {
                return element;
            }
        };
        RedBlackTree<Key, Key, SetKeyExtractor> rbTree;
    public:
        // Both iterator types are const_iterators to prevent modification.
        typedef typename decltype(rbTree)::const_iterator iterator;
        typedef typename decltype(rbTree)::const_iterator const_iterator;

        iterator begin() const { return rbTree.begin(); }
        iterator end() const { return rbTree.end(); }

        std::pair<iterator, bool> insert(const Key& element) {
            return rbTree.Insert(element);
        }
    };
}

In the Set implementation, both iterator and const_iterator are aliased to the RBTree's const_iterator. This prevents modification of set elements. The RBTree's Insert method returns a pair<TreeNode*, bool>, which the set::insert can implicitly convert to its required pair<iterator, bool> return type without a type mismatch.