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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: MI is sloppy (was: Construction initialization problem)
Date: Wed, 10 Dec 2008 18:40:46 -0600
Organization: Jacob Sparre Andersen
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Date: 2008-12-10T18:40:46-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:d0goewygto13.10nsyzpabm3vn.dlg@40tude.net...
> On Fri, 5 Dec 2008 19:42:40 -0600, Randy Brukardt wrote:
>
>> A waste of effort. I don't believe in multiple inheritance (in any form); 
>> it
>> seems to me to be an excuse for sloppy design.
>
> It is like saying that a record with two components is a sloppy design.
> Either inheritance is a rubbish concept or else it is multiple.
>
> My pet example of MI is:
>
>   type In_File is ...;
>   procedure Get (File : in out Input_File; Item : out Data);
>
>   type Out_File is ...;
>   procedure Put (File : in out Output_File; Item : Data);
>
>   type Inout_File is .. ?
>
> Is it sloppy?

I tend to think so. These are insufficiently different to be types; there 
should only be one type and different subtypes. Subtypes imply runtime 
checks, but with good contracts most such errors can still be detected by 
tools. And you don't have the goofy restrictions that come with trying to 
make things separate types that aren't logically separate.

This is very much like the attempt to statically check accessibility 
(lifetime) of objects. It doesn't work, at least not in general. And we have 
much better technology in terms of detecting errors without goofy 
restrictions than we did when these rules were defined, so why not use 
them??

                               Randy.