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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada noob here! Is Ada widely used?
Newsgroups: comp.lang.ada
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Date: Sun, 6 Jun 2010 11:22:07 +0200
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Date: 2010-06-06T11:22:07+02:00
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On Sun, 06 Jun 2010 10:25:11 +0200, Yannick Duchêne (Hibou57) wrote:

> Le Sun, 06 Jun 2010 09:46:28 +0200, Dmitry A. Kazakov  
> <mailbox@dmitry-kazakov.de> a écrit:
>> = exponentially
>>
>> http://en.wikipedia.org/wiki/Geometric_progression
> OK, a quasi-synonym

And, maybe, you have a chance of having it not geometric, but
combinatorial... (:-))

http://en.wikipedia.org/wiki/Combinatorial_explosion

>>> I remember in the past (past year I think), we talked around generics
>>> hierarchy and generic packages as formal parameters. You had warned  
>>> about
>>> possible complexity explosion in this area: is this about the same ?
>>
>> Yep. Once generic always generic. Two generics make four instantiations.
>> And the mill starts milling...
> This path is not the only one way. There can be instantiations to be used  
> as basic components. Generics does not provide just a way to declare  
> things, this also gives a way to implement, and implementation is an  
> hidden thing (or else private at least). Generic origin of a type can be  
> hidden (as an example) ; while obviously, some relationships are then lost.
> 
> This can lead into an combinatorial explosion, right ; except “can” is not  
> “always” (while I agree to say it can comes faster than supposed, and  
> recurrence/recursivity should be in mind here while designing).

Normally you wanted to postpone instantiation to as late as possible. But
any delayed instantiation means a generic formal parameter in another
generics and so it leads to the explosion at the point where you ultimately
instantiate the mess. This is not a problem for small projects. That is why
most Ada people don't see generics as a problem.

Add here that generics are non-testable. You can test instances, you cannot
generics. Then Ada has been drifting towards C++ in the sense what promises
gives you a successful compilation of the generic body, little, very
little, nothing...

But if you force yourself to instantiate earlier, you get a very fragile
design. Generics are against good design.

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