I'm reading through Algorithms Fourth Edition by Sedgewick and doing some of the practice exercises in C++11 instead of Java. Exercise 1.3.29 is to write a Queue that uses a circular linked list, keeping only one Node instance variable (last).

All comments are welcome, but especially ones focusing on advanced C++ techniques as well as the algorithm itself.

#ifndef QUEUE_HH
#define QUEUE_HH

#include <cstddef>
#include <stdexcept>

template<class T>
class Queue {
public:

    Queue()
    : _last(nullptr)
    {}

    void enqueue(T value)
    {
        // Create a new node, not yet linked to anything
        Node* node = new Node{value, nullptr};

        if(is_empty()) {
            // Only node in the list, link it to itself
            node->next = node;
        } else {
            // Link the new node to the start of the list
            node->next = _last->next;

            // Add the new node to the end of the list
            _last->next = node;
        }

        _last = node;
    }

    T dequeue()
    {
        if(is_empty()) {
            throw std::out_of_range("Empty queue");
        }

        // Get the first node in the list
        Node* node = _last->next;

        // Unlink the node by pointing last to the next node
        _last->next = node->next;

        // If we're removing the only node in the list, set last node to nullptr
        if(node == _last) {
            _last = nullptr;
        }

        // Retrieve the value before deleting the node
        int value = node->value;

        delete node;
        return value;
    }

    size_t size() const
    {
        if(is_empty()) {
            return 0;
        }

        // Start at last node, count iterations until last node is reached again
        size_t count = 0;
        Node* current = _last;
        do {
            count++;
            current = current->next;
        } while(current != _last);

        return count;
    }

    bool is_empty() const
    {
        return _last == nullptr;
    }

private:

    struct Node
    {
        T value;
        Node* next;
    };

    Node* _last;
};

#endif // QUEUE_HH