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From: Vinzent Hoefler <ada.rocks@jlfencey.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada 200X
Date: Mon, 02 Jun 2003 16:31:49 +0200
Organization: JeLlyFish software
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Date: 2003-06-02T16:31:49+02:00
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Robert I. Eachus wrote:

>Larry Kilgallen wrote:
>
>> The lack of a construct to specify "corresponding method of ancestor"
>> seems to me to be what breaks information hiding.
>
>Oh, that is so easy that I never thought of people having problems with=20
>it.  I'll give an example:
>
>type Foo is tagged...
>
>procedure Bar(F: in out Foo);
>...
>
>type New_Foo is new Foo with...
>
>procedure Bar(F: in out New_Foo);
>...
>
>procedure Bar(F: in out New_Foo) is
>begin
>    Do(Something_Special);
>    Bar(Foo(F)); -- view conversion
>    Do(Something_Else_Special);
>end Bar;
>
>The view conversion passes the Foo part of a New_Foo object to the=20
>parent Bar by reference.

Yeah, but what happens if you insert

|type Baz is new Foo with ...
|
|procedure Bar (F : in out Baz);
|
|type New_Foo is new Baz with ...

is that you have to change every single view conversion in New_Foo's
methods from

|Bar (Foo (F));

to

|Bar (Baz (F));

Because the view conversion to a grandparent is of course allowed,
this is little tricky if not to say error prone sometime.

Well, yes, I know, you should always design your object hierarchy
beforehand. ;-)


Vinzent.

--=20
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