Re: why "unconstrained subtype in component declaration" while said component given default value ?

[Simon Wright <simon@pushface.org>]

Mehdi Saada <00120260a@gmail.com> writes:

> Also, there's something that would be really cool, and I'm curious why
> it could not be allowed: Why can't we provide a private constrained
> subtype, of an inconstrained private type ?
>
> package III is
>    type A (<>) is private;
>    subtype B is A;  -- should be a constrained subtype
> private
>    function Donne_String (N : Positive) return String;
>    type A (N: Positive) is record
>       II : Integer;
>       Chaine : String(1..N) := Give_String(N);
>    end record;
> end III;

The Booch Components originally had the maximum length of a bounded
container fixed at generic instantiation, which is a very limiting
design. So as to avoid forcing all users to rework, I ended up with, for
example,

generic
   Maximum_Size : Positive;
package BC.Containers.Collections.Bounded is

   type Unconstrained_Collection
     (Maximum_Size : Positive) is new Abstract_Collection with private;

   subtype Collection
      is Unconstrained_Collection (Maximum_Size => Maximum_Size);

[...]

   function "=" (Left, Right : in Unconstrained_Collection) return Boolean;

[...]

   procedure Insert (C : in out Unconstrained_Collection; Elem : Item);
   --  Add the item to the front of the collection.