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Newsgroups: comp.lang.ada
Subject: Re: array of generic packages?
References: <4151be92@dnews.tpgi.com.au>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: Wed, 22 Sep 2004 20:26:40 +0200
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Date: 2004-09-22T20:29:24+02:00
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"a malkiel" writes:
> hi im somewhat new to ada. i've been trying to nut this one but can't seem 
> to. Would anyone know if defining an "array of generic packages" is 
> possible? What im looking for is something of the nature:
>
> type shape_type is (circle, triangle);
> package shapePointer(1) is new shape(circle);
> package shapePointer(2) is new shape(triangle);
>
> thanks in advance.
> ciao, andrew 

No, you cannot have an array of generic packages.  You can only have
arrays of objects; objects are constants and variables.  You can
create a generic package that declares a new type of arrays, like so:

generic
   type Element_Type is private;
package Generic_Arrays is
   type Array_Type is array (Positive range <>) of Element_Type;
end Generic_Arrays;

type Triangle is ...

package Arrays_Of_Triangles is
    new Generic_Arrays (Element_Type => Triangle);

My_Triangle : Triangle;
My_Array : Arrays_Of_Triangles.Array_Type := (1 => My_Triangle);

However, the generic package is not really all that useful if all you
want is to declare new array types.  You'd be better off doing just:

type Array_Of_Triangles is array (Positive range <>) of Triangle;
type Array_Of_Circles is array (Positive range <>) of Circle;

which does not require a generic.

-- 
Ludovic Brenta.