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Date: Fri, 03 Aug 2012 15:18:01 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: Abstraction over container iterators
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Date: 2012-08-03T15:17:56+02:00
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On 03.08.12 14:52, Dmitry A. Kazakov wrote:
> On Fri, 3 Aug 2012 05:01:41 -0700 (PDT), ms wrote:
> 
>> What we have here is an example package fairly well illustrating my
>> problem. I'm storing some environment variables in Hashed_Map, but I want
>> to build a abstraction layer over the standard container, so I can in
>> future change the underlaying container without changing any code in my
>> package's customers.
>>
>> Getting and setting variables is easy - as declared above. The real
>> problem is iterating. I'd like to let my package's customers to iterate
>> over the environment and get both key and value for each element easily.
> 
> Add the iteration abstraction to the package. The implementation would both
> do both the container and the iterator.

2nd. The type has-a container, so it has-a cursor as well.

Your type could supply a call-back style iteration mechanism, too,
such as

 generic
   with Customery_Query (Name : Unbounded_String);
 procedure For_Every_Name (E : Environment);

Or use an anonymous procedure pointer instead of a template.