Method push

listings/listing_6.5.cpp:35–44

    }
    
    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;
    }
};