Re: slice'access?

[tmoran@acm.org]

> > Is there a nice way to create an access to a slice? eg
> The answer of course is no. The RM does not allow this
> and if you think for just a moment it is obvious why. The
> usual representation of bounds for an array is to have the
> bounds immediately before the data, but of course that

  The problem at hand is that a package maintains a private data
structure which contains, among other things, long strings.  I want
(read only) access to one of those strings.  Of course it's
possible to call the data package and have it return a string,
  subtype card is string(1 .. 80);
  function get_card(param) return card;
but speed matters.  It would be faster to get a pointer
  function get_card_pointer(param) return ptr_type;
For instance, getting character(8) of the card could be done with
  get_card(param)(8)
but
  get_card_pointer(param)(8)
is likely to be a lot faster.
  Using a fixed length subtype and system.address_to_access_conversions, a
quick test shows it works fine on two different compilers.  Or I can call
a subprogram and pass the slice, eg
  procedure callback_to_process_the_card(s : in card);
  fetch_card(param, callback_to_process_the_card'access);
and be very surprised if it's passed by copy.  Neither of those techniques
is very nice.  Is there a NICE way to create an access to a slice?