20 class Counter : public Counter_base
23     Counter() : data_()                             { ++gConstructed; }  in Counter()  function
24     Counter(const T &data) : data_(data)            { ++gConstructed; }  in Counter()  function
25     Counter(const Counter& rhs) : data_(rhs.data_)  { ++gConstructed; }  in Counter()  function
26     Counter& operator=(const Counter& rhs)          { data_ = rhs.data_; return *this; }
28     Counter(Counter&& rhs) : data_(std::move(rhs.data_))  { ++gConstructed; }  in Counter()  function
29 …  Counter& operator=(Counter&& rhs) { ++gConstructed; data_ = std::move(rhs.data_); return *this; }
31     ~Counter() { --gConstructed; }  in ~Counter()
35     bool operator==(const Counter& x) const {return data_ == x.data_;}
36     bool operator< (const Counter& x) const {return data_ <  x.data_;}
47 struct hash<Counter<T> >
49     typedef Counter<T> argument_type;
52     std::size_t operator()(const Counter<T>& x) const {return std::hash<T>()(x.get());}