Re: Null Range in Unconstrasined Array

[Adam Beneschan <adam@irvine.com>]

On Sep 6, 5:41 am, Robert A Duff <bobd...@shell01.TheWorld.com> wrote:
> There are several ways to implement that.
> For example, the procedure could be passed the bounds as separate
> parameters, in two registers.  I don't consider that to
> be "memory allocated for My_Array", because it is not
> allocated when the compiler sees My_Array -- it is allocated
> when the compiler sees a call (and separately for each call).
> In this case, My_Array'Address = X'Address is likely.

To elaborate on this a bit further: Suppose you define a record type
for reading a file with Ada.Direct_IO, that looks something like this:

  type Employee_Data is record
      Name     : String (1 .. 50);
      Address1 : String (1 .. 40);
      Address2 : String (1 .. 40);
      City     : String (1 .. 30);
      State    : String (1 .. 2);
      ...
  end record;

(Reminds me of my COBOL programming days...)  Anyway, it would be very
unexpected for the compiler to put two extra integers in the record
for each of these strings, and it would mess up your file I/O.  But
you have to have the ability to pass any of those fields to a
subprogram with a parameter type "String", and the bounds have to be
passed to the subprogram somehow.  I think it's most likely that the
bounds will be passed separately, as Bob suggested, either by passing
them in separate registers, creating a three-word temporary structure
that contains the bounds and a pointer to the data and passing the
address of that structure (with that structure disappearing after the
subprogram returns), creating a two-word structure with the bounds and
passing the address of that in a register, etc.  Something along those
lines.  But I'd actually be surprised if *any* implementation
allocated extra space in an Employee_Data record to hold the bounds of
each field.

                                             -- Adam