Re: [Q] Problem with Array Concatenation?

[mheaney@ni.net (Matthew Heaney)]

In article <33c280c8.418253@news.demon.co.uk>, john@assen.demon.co.uk (John
McCabe) wrote:

>procedure Test is
>   type Arr_Type is array (1 .. 100) of Integer;
>
>   Src_Array : Arr_Type;
>   Dst_Array : Arr_Type;
>begin
>   for Index in 1 .. 100 loop
>      Src_Array (Index) := Index;
>   end loop;
>   Dst_Array := (others => 0);
>
>   Dst_Array := Src_Array (51 .. 100) & Src_Array (1 .. 50);
>end Test;

As Tuck pointed out, the concatenation will raise Constraint_Error, even
though this is a legal Ada program.  But even in Ada 83, there is a simple
fix: make the array type unconstrained:

declare
   type AT is array (Positive range <>) of Integer;

   SA : AT (Positive range 1 .. 100);
   DA : AT (SA'Range);
begin
   for Index in SA'Range loop
      SA (Index) := Index;
   end loop;

   DA := SA (51 .. 100) & SA (1 .. 50);
end;

There's another way to make the fix, by manually sliding the initial substring:

declare
   type AT is array (Positive range 1 .. 100) of Integer;

   SA : AT;
   DA : AT;
   subtype Slided is AT (1 .. 50);
begin
   ...
   DA := Slided (SA (51 .. 100)) & SA (1 .. 50);
end;

In Ada 83 the 2nd substring will be automatically slided.

- Matt

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Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271