38 // Queue is a simple queue implemented as a singled-linked list.
42 class Queue;  variable
44 // QueueNode is a node in a Queue, which consists of an element of
48   friend class Queue<E>;  variable
54   // Gets the next node in the queue.
73 class Queue {
75   // Creates an empty queue.
76   Queue() : head_(nullptr), last_(nullptr), size_(0) {}  in Queue()  function
78   // D'tor.  Clears the queue.
79   ~Queue() { Clear(); }  in ~Queue()
81   // Clears the queue.
103   // Gets the first element of the queue, or NULL if the queue is empty.
107   // Gets the last element of the queue, or NULL if the queue is empty.
111   // Adds an element to the end of the queue.  A copy of the element is
112   // created using the copy constructor, and then stored in the queue.
113   // Changes made to the element in the queue doesn't affect the source
128   // Removes the head of the queue and returns it.  Returns NULL if
129   // the queue is empty.
148   // Applies a function/functor on each element of the queue, and
149   // returns the result in a new queue.  The original queue is not
152   Queue* Map(F function) const {  in Map()
153     Queue* new_queue = new Queue();  in Map()
163   QueueNode<E>* head_;  // The first node of the queue.
164   QueueNode<E>* last_;  // The last node of the queue.
165   size_t size_;  // The number of elements in the queue.
167   // We disallow copying a queue.
168   Queue(const Queue&);
169   const Queue& operator = (const Queue&);