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From: "Dr. Michael Paus" <paus@ib-paus.com>
Newsgroups: comp.lang.ada
Subject: Re: Small question concerning use
Date: Thu, 18 Oct 2001 20:46:34 +0200
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Date: 2001-10-18T18:42:34+00:00
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I wonder why in these discussions about the use of "use" people
always use more or less trivial examples. I think for these
examples the issue is more or less a matter of taste. The real
problem with "use" arrises if you make intensive use of object
oriented features in Ada. E.g. if you have a package "My_Pack_A"
in which you define a tagged type "My_Class_A" and another
package "My_Pack_B" in which you define a tagged type "My_Class_B"
which is derived from "My_Class_A". Now assume that B inherits
a method "My_Method" from A. If you now have an instance
of the B class and you want to call one of its methods, say

   B : My_Pack_B.My_Class_B;
   xxx.My_Method(B, Some_Value);

So what is the right package name to put in for xxx? When you
have found out you certainly admit that this may be quite
cunfusing although there is of course a clear logic behind it.

My experience is that if you intensively use object oriented
features the use of "use" quickly becomes a pain in the ...:-)
And if you are interested I can give you examples where in this
particular case the use of "use" resulted in severe bugs in the
code which were very hard to track down. Also the use of "use type"
does not help here because it only makes the operators of a type but
not the primitive methods of a class type visible.

Michael