Re: Anonymous array clarification.

["Phil Thornley" <phil.thornley@baesystems.com>]

"McDoobie" <chris@dont.spam.me> wrote in message
news:tY1g7.45466$K6.17744072@news2...
> In Ada one can declare anonymous arrays (an array without a type
assigned
> to it.)  However what would such an array be used for, and are the
bounds
> on it's use the same as for any other type of array.
>
> I guess what I'm asking is if I declare an array such as
>
> some_array : array(1..N);
>

You have to give the component type as well:

some_array : array(1..N) of Integer;  -- or whatever

so the question of how the components are stored doesn't arise.

On the question of what they are used for, I most commonly use them for
look-up tables.

   type Day is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);

   Tomorrow : constant array (Day) of Day
                     := (Tue, Wed, Thu, Fri, Sat, Sun, Mon);

(which avoids a lot of stuff about 'Succ and worrying about
wrap-around).

You can't declare two anonymous arrays of the same type even in the same
declaration:

   A, B : array (1 .. 5) of Integer;

A and B are if different anonymous types and so can't be assigned
(i.e. A := B; is an illegal statement).

Note that an anonymous array can never be passed as the parameter of a
subprogram as you can't name the parameter type.

Cheers,

Phil

--
Phil Thornley
Programmes, Engineering
Warton