Small detail: the test could could test what the value of x++ is, like this:
    cout << "Before x = " << x << endl;
    cout << "In between x = " << x++ << endl;
    cout << "After x = " << x << endl;
It works correctly. (output is 1, 1, 2)

The helper class could be made a seperate class with a helper function, like this:

    template<class T> 
    struct postfix_incrementer: public T
    {
        postfix_incrementer(T &rhs): T(rhs) // call the copy constructor!
        {
            ++rhs;
        }
    };

    template<class T> 
    T postfix_increment(T& rhs)
    {
        return postfix_incrementer<T> (rhs);
    }

Then you can replace the postfix increment operator with

    number operator++(int)
    { return postfix_increment(*this); }

The only thing is that I do not clearly see if there's still the copying
advantage...
Is this useful for the utility library?

Richard Peters

----- Original Message -----
From: "Powell, Gary" <powellg@[...].com> 


>  Ah but you can fix the need to call the copy constructor by using a
>  helper template class instead.
>  (I credit this to Joel's suggestion!)
> 
>                -Gary-
> 
>  PS
>   Of course if this doesn't really work, I'm to blame.
>  -----------------------------------------------
> 
>  class number {
>  private:
> 
>      template<class T>
>      struct helper_class : public T
>      {
>          helper_class(T &rhs): T(rhs) // call the copy constructor!
>          {
>              ++rhs;
>          }
>      };
> 
>  int value;
> 
>  public:
>     explicit number(int rhs = 0)
>         : value(rhs) {}
> 
>    number &operator++()
>        { ++value; return *this; }
> 
>    number operator++(int)
>        { return helper_class<number>(*this); }
> 
>    friend
>    ::std::ostream & operator<<(::std::ostream &os, number const &rhs)
>    {
>      os << rhs.value;
>      return os;
>    }
>  };
> 
>  int main()
>  {
>      using ::std::cout;
>      using ::std::endl;
> 
>      number x(1);
> 
>      cout << "Before x = " << x << endl;
>      x++;
> 
>      cout << "After x = " << x << endl;
>      x++;
>      cout << "After x = " << x << endl;
> 
>      return 1;
>  }


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