Re: Converting access values

[Nick Roberts <nick.roberts@acm.org>]

Mark Lorenzen <mark.lorenzen@ofir.dk> wrote:

> As I said in another posting, I am going for a design like this:
> 
> type Buffer_Slice is
>    record
>      Data  : Buffer_Ptr;
>      First : Ada.Streams.Stream_element_Offset;
>      Last  : Ada.Streams.Stream_element_Offset;
>    end record;
> ...
> It solves the problem, but exposes a bit more information to the clients
> than necessary. It is very easy for a client to address a slice outside
> the bounds:
> ...

Since you put it that way, I see your point. I suppose it is an area where
Ada fails to provide a level of abstraction that perhaps it should. It's
almost as if we want a new kind of access type, the 'slice access' type,
that can point to a slice of an array, e.g.:

   type Buffer_Slice is access range Stream_Element_Array;

objects of which, when dereferenced, can be used anywhere a
Stream_Element_Array object can, and have the same attributes (First and
Last and so on).

-- 
Nick Roberts