----- Original Message ----- From: "Angel Tsankov" <fn42551@fmi.uni-sofia.bg> To: <boost@lists.boost.org> Sent: Tuesday, July 22, 2008 9:37 PM Subject: Re: [boost] [unnullable_ptr] Proposal for a new library
Mathias Gaunard wrote:
Do you still provide pointer arithmetic and implicit upcasting?
Yes, implicit upcasting as well as the usual casts to void*, and T const* are supported (I've even written several unit tests especially to check the conversions). Implicit conversion from array to unnullable_ptr is also supported.
As for pointer arithmetic, I've not yet needed it to work with unnullable_ptr's, so I've not considered implementing it. Nevertheless, it turns out that pointer arithmetic is partially supported (via the convertion operator from unnullable_ptr to C pointer); this is to say that subtracting unnullable_ptr's works, but subtracting int's from (or adding int's to) unnullable_ptr's doesn't yet. In fact, subtracting an int from (as well as adding an int to) an unnullable_ptr might result in a null pointer so the result need to be checked. However, the current implementation of unnullable_ptr is exactly as effective as a built-in C pointer (or at least allows instances of unnulable_ptr to be that effective) and I would like to keep it that way. So, subracting and adding int's will probably not be supported, unless a zero-overhead way is devised to guarantee unnullability of the result from these operations.
What is the expected calue of c? It is not 0? T t; UnnullablePtr<T> a(t); UnnullablePtr<T> b(t); UnnullablePtr<T> c(t); c=a-b; Vicente