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

["Randy Brukardt" <randy@rrsoftware.com>]

"A. Cervetti" <andrea.cervetti@gmail.com> wrote in message 
news:e3a1f97e-7cbd-4327-aef6-c18ca9e74bc2@googlegroups.com...
>use attribute 'Address:
>
>with Ada.Text_IO; use Ada.Text_IO;
>with Ada.Float_Text_IO; use Ada.Float_Text_IO;
>with Ada.Numerics.Generic_Real_Arrays;
>
>procedure Double_Array is
>   package Real_Array is new Ada.Numerics.Generic_Real_Arrays(Float);
>   use Real_Array;
>
>   x : Real_Vector(0 .. 4) := (1.0, 2.0, 3.0, 4.0, 5.0);
>   y : Real_Vector(1 .. 5);
>   for Y'Address use X'Address; -- <<<<<<<<<<<<<<<<<<<<

An evil and not guaranteed to work on all implementation technique.

The OP just needs to use an appropriate type conversion to change the bounds 
of their array (odd no one has mentioned that):

If one has:

   subtype RV1_5 is Real_Vector(1..5);

Then the type conversion:
    RV1_5(X) has the new bounds, and (by itself) doesn't copy any memory.

Thus, using a subprogram to temporarily bind the object shouldn't result in 
any copying of the data (no guarantees, of course, but it will always work - 
rememberm avoid premature optimization!):

    procedure Do_Y (Y : RV1_5) is
    begin
         -- Operations on Y.
    end Do_Y;

    ...
    Do_Y (RV1_5(X));

This is the best way to change the bounds of an array (or part of an array) 
in Ada.

                                                            Randy.



begin
   X(0) := 20.0;
   Put(X(0), 0, 0, 0); New_Line;
   Put(Y(1), 0, 0, 0); New_Line;
end Double_Array;

A.