"Philippe A. Bouchard" <philippeb@[...].ca>  wrote in message
news:aj8m3k$oce$1@[...]..
>  > I'm not sure if this ptr<> type under discussion works this way, but in
>  > general you can't conformingly use char* arithmetic with offsets to find
>  > the sub-parts of non-POD types.
> 
>  The offsets are what static_cast<>s return.  I cheat in the syntax when I
>  say ptr_base<T, __false_type>::m_ptr is of type T *; it's just to make the
>  code cleaner.

Umm...my understanding is that what Dave is talking about is exactly
what you are doing.  After all, what is the business with
reinterpret_cast<char*>  to do offset arithmetic?

>  [...]
>  template <typename T>
>      struct ptr_block
>      {
>          int m_counter;
>          int m_typeid;
> 
>          union
>          {
>              int;
>              T;
>          } m_object;
>      };
> 
>  But operator new (size_t, rc_type const &) won't be easy to implement
>  because size_t is not a compile-time constant.

I spent a while trying to see if it was possible to make this "invisible
count
wrapper", but ran into the same problem: you need to know the type,
because operator new only provides the size of the type as a runtime
value.  I don't see how you can make a safe, conforming, portable count
wrapper without explicitly naming the type somewhere (like your original
placement new operator which passed in the type).

Dave





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