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From: Marek <ficorax@gmail.com>
Newsgroups: comp.lang.ada
Subject: 2-dimensional view on 1 dimensional array
Date: Sun, 23 Oct 2022 14:31:22 +0200
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Hi.
Assume we have:

     generic
        type T is private;
        type T_Array is array (Natural range <>) of aliased T;
        type T_Array_Access is access all T_Array;
     package Buffers is

        type Row_Array is array (Natural range <>) of aliased 
T_Array_Access;

        type Row_Array_Access is access all Row_Array;

        type Buffer is tagged
           record
              Raw_Buffer : T_Array_Access   := null;
              Rows_Table : Row_Array_Access := null;
              Rows       : Natural          := 0;
              Columns    : Natural          := 0;
              Step       : Integer          := 0;
              Max_Rows   : Natural          := 0;
           end record;

        procedure Init
          (This    : in out Buffer;
           Buffer  :        T_Array_Access;
           Rows    :        Natural;
           Columns :        Natural;
           Step    :        Integer);

        procedure Set_Value
          (This  : in out Buffer;
           Value :        T);

     end Buffers;

..and:

     with Ada.Unchecked_Deallocation;

     package body Buffers is

        type T_Access is access all T;

        ------------
        --  Init  --
        ------------

        procedure Init
          (This    : in out Buffer;
           Buffer  :        T_Array_Access;
           Rows    :        Natural;
           Columns :        Natural;
           Step    :        Integer)
        is
           procedure Free is
             new Ada.Unchecked_Deallocation (Row_Array, Row_Array_Access);

           Row_Index : Integer := 0;
        begin
           This.Raw_Buffer := Buffer;
           This.Rows       := Rows;
           This.Columns    := Columns;
           This.Step       := Step;

           if Rows > This.Max_Rows then
              if This.Rows_Table /= null then
                 Free (This.Rows_Table);
              end if;

              declare
                 New_Rows : constant Row_Array_Access :=
                              new Row_Array (0 .. Rows - 1);
              begin
                 This.Rows_Table := New_Rows;
                 This.Max_Rows := Rows;
              end;
           end if;

           for H in 0 .. Rows - 1 loop
              declare
                 Row_Start : constant T_Access :=
                               This.Raw_Buffer (Row_Index * Step)'Access;
              begin
                 This.Rows_Table (H) := ...  -- What code here?

                 Row_Index := Row_Index + 1;
              end;
           end loop;

        end Init;

        -----------------
        --  Set_Value  --
        -----------------

        procedure Set_Value
          (This  : in out Buffer;
           Value :        T)
        is
        begin
           if This.Rows > 0 then
              for Y in 0 .. This.Rows - 1 loop
                 declare
                    Row : constant T_Array_Access := This.Rows_Table (Y);
                 begin
                    if This.Step > 0 then
                       for X in 0 .. This.Step - 1 loop
                          Row (X) := Value;
                       end loop;
                    end if;
                 end;
              end loop;
           end if;
        end Set_Value;

     end Buffers;

and finally:

     with Buffers;

     procedure Test is

        type Float_Array is array (Natural range <>) of aliased Float;

        type Float_Array_Access is access all Float_Array;

        package Buffer_Package is
          new Buffers (Float, Float_Array, Float_Array_Access);

        use Buffer_Package;

        A : aliased Float_Array := (0 .. 99 => 0.0);
        B : Buffer_Package.Buffer;
     begin

        B.Init (A'Access, 10, 10, 10);
        B.Set_Value (10.0);
     end Test;

Is there any possibilities to get this working?
Idea is to have another (2 dimensional) view on 1 dimensional array.
Unchecked_Conversion is not working (different sizes of objects).
Address_To_Access conversion also (unconstrained array);

Marek