40 // Queue is a simple queue implemented as a singled-linked list.
44 class Queue;  variable
46 // QueueNode is a node in a Queue, which consists of an element of
50   friend class Queue<E>;  variable
56   // Gets the next node in the queue.
74 class Queue {
77   // Creates an empty queue.
78   Queue() : head_(NULL), last_(NULL), size_(0) {}  in Queue()  function
80   // D'tor.  Clears the queue.
81   ~Queue() { Clear(); }  in ~Queue()
83   // Clears the queue.
105   // Gets the first element of the queue, or NULL if the queue is empty.
109   // Gets the last element of the queue, or NULL if the queue is empty.
113   // Adds an element to the end of the queue.  A copy of the element is
114   // created using the copy constructor, and then stored in the queue.
115   // Changes made to the element in the queue doesn't affect the source
130   // Removes the head of the queue and returns it.  Returns NULL if
131   // the queue is empty.
150   // Applies a function/functor on each element of the queue, and
151   // returns the result in a new queue.  The original queue is not
154   Queue* Map(F function) const {  in Map()
155     Queue* new_queue = new Queue();  in Map()
164   QueueNode<E>* head_;  // The first node of the queue.
165   QueueNode<E>* last_;  // The last node of the queue.
166   size_t size_;  // The number of elements in the queue.
168   // We disallow copying a queue.
169   Queue(const Queue&);
170   const Queue& operator = (const Queue&);