Method push

listings/listing_6.4.cpp:43–56

    }
    
    void push(T new_value)
    {
        std::unique_ptr<node> p(new node(std::move(new_value)));
        node* const new_tail=p.get();
        if(tail)
        {
            tail->next=std::move(p);
        }
        else
        {
            head=std::move(p);
        }
        tail=new_tail;
    }
};