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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Generic package parameters not externally visible : what's the
  rational ?
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Date: Fri, 30 Oct 2009 20:32:12 +0100
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Date: 2009-10-30T20:32:13+01:00
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On Fri, 30 Oct 2009 06:25:21 -0400, Stephen Leake wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> My take is that any generic code is potentially broken. Anyone who uses
>> generics beyond very trivial cases should know that, and mentally prepare
>> himself to fix his code over and over again.
> 
> That is certainly not my experience. I use generics extensively; it's
> one of the best features of the language.

Do you use generic in other generics?

How does look the hierarchy matrix of?

This requires a bit explanation. A set of generics sharing some common
parameter (like the number type in a generic matrix package) are kind of
class, i.e. they declare sets of types dependant on the parameter (like
vector, matrix etc). I call this almost "trivial".

Non-trivial it becomes when you have several such axes.

Here is an example of a mesh of generic packages with 4 axes:

   http://www.dmitry-kazakov.de/ada/fuzzy.htm#8

Note that semantically the example is quite simple, almost evident. Its
implementation and use is horrific. I would never consider it "fixed".

As for being the "best language feature", I hope that you would easily find
lots of more useful and advanced Ada features. What about unconstrained
types? User-defined numeric types? Packages (vs. types) as encapsulation
modules? If any of these were removed it would not be Ada. On the contrary,
Ada without generics sounds quite plausible to me.

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