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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Generic procedures and their parameters
Newsgroups: comp.lang.ada
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References: <edm273$fee$1@sunnews.cern.ch>
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Date: Thu, 7 Sep 2006 09:47:45 +0200
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Date: 2006-09-07T09:47:45+02:00
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On Wed, 6 Sep 2006 19:47:14 -0700, Steve wrote:

> "Maciej Sobczak" <no.spam@no.spam.com> wrote in message 
> news:edm273$fee$1@sunnews.cern.ch...
>> Hi,
>>
>> I have found the following signature for the sorting procedure:
>>
>> eneric
>>    type Index_Type   is (<>);
>>    type Element_Type is private;
>>    type Array_Type   is array (Index_Type range <>) of Element_Type;
>>    with function "<" (Left, Right : in Element_Type) return Boolean is <>;
>> procedure Sort(To_Sort : in out Array_Type);
>>
>> My question is: what's the purpose of the third parameter (Array_Type)? 
>> Isn't it implied by the first two and therefore just redundant?
> 
> I prefer:
> 
> generic
>     type Index_Type is (<>);
>     type Collection_Type is private;
>     firstIndex : Index_Type;
>     lastIndex : Index_Type;
>     with function In_Order( list : Collection_Type; i, j : Index_Type ) 
> return Boolean;
>     procedure Swap( list : in out Collection_Type; i, j : Index_Type );
> procedure Sort( list : in out Collection_Type );
> 
> This avoids the declaration of the array altogether, and is usable for any 
> list that may be referenced by index.

Ah, that's an "abstract generic array" thing. If more that just Sort is
needed one goes as:

generic
   type Index_Type is (<>);
   type Element_Type is private;
   Null_Element : Element_Type;
   type Collection_Type is private;
   with function First (X : Collection_Type) return Index_Type is <>;
   with function Last (X : Collection_Type) return Index_Type is <>;
   with function Get (X : Collection_Type) return Element_Type is <>;
   with procedure Set (X : in out Collection_Type; Y : Element_Type) is <>;
package Generic_Collection is
   -- Nothing here. It is an "abstract" package
end Generic_Collection;

Then Sort becomes a child:

generic
   with function "<" (Left, Right : Element_Type) return Boolean;
procedure Generic_Collection.Sort (X : in out Collection_Type);

Unfortunately, Element_Type reappears.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de