add original source

source/listing_6.5.cpp

@@ -0,0 +1,46 @@
+#include <memory>
+template<typename T>
+class queue
+{
+private:
+    struct node
+    {
+        std::shared_ptr<T> data;
+        std::unique_ptr<node> next;
+    };
+    
+    std::unique_ptr<node> head;
+    node* tail;
+    
+public:
+    queue():
+        head(new node),tail(head.get())
+    {}
+
+    queue(const queue& other)=delete;
+    queue& operator=(const queue& other)=delete;
+
+    std::shared_ptr<T> try_pop()
+    {
+        if(head.get()==tail)
+        {
+            return std::shared_ptr<T>();
+        }
+        std::shared_ptr<T> const res(head->data);
+        std::unique_ptr<node> const old_head=std::move(head);
+        head=std::move(old_head->next);
+        return res;
+    }
+    
+    void push(T new_value)
+    {
+        std::shared_ptr<T> new_data(
+            std::make_shared<T>(std::move(new_value)));
+        std::unique_ptr<node> p(new node);
+        tail->data=new_data;
+        node* const new_tail=p.get();
+        tail->next=std::move(p);
+        tail=new_tail;
+    }
+};
+