Re: How to access an array using two different indexing schemes

[Jerry <list_email@icloud.com>]

On Friday, November 24, 2017 at 3:15:35 PM UTC-7, Robert A Duff wrote:
> Jerry writes:
> 
> > On Friday, November 24, 2017 at 10:37:30 AM UTC-7, A. Cervetti wrote:
> >>    for Y'Address use X'Address; -- <<<<<<<<<<<<<<<<<<<<
> 
> > Nice. Thank you. That solves the "version control" or "bookkeeping"
> > problem, but it still requires allocating double memory, for y.
> 
> No, X and Y are allocated at the same address.
> That's the point of this low-level hack.
> 
> - Bob

Oh. That seems to solve all my problems. I did it this way:

with Ada.Numerics.Long_Real_Arrays; use Ada.Numerics.Long_Real_Arrays;
procedure Double_Array_1 is
    x : Real_Vector(-4 .. 3);
    y : Real_Vector(0 .. 7);
    for y'Address use x'Address; -- <<<< 'Address trick
begin
    null;
end Double;

Now I wonder if I could get greedy.

I frequently allocate memory for arrays from the heap, as discussed previously on this list, like this:

with Ada.Numerics.Long_Real_Arrays; use Ada.Numerics.Long_Real_Arrays;
procedure Double_Array_2 is
    type Real_Vector_Access is access Real_Vector;
    x_Ptr : Real_Vector_Access := new Real_Vector(-4 .. 3);
        x : Real_Vector renames x_Ptr.all;
    y_Ptr : Real_Vector_Access := new Real_Vector(0 .. 7);
        y : Real_Vector renames y_Ptr.all;
begin
    null;
end Double_Array_2;

How would I use the 'Address trick in this situation?

Jerry