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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: a new language, designed for safety !
Date: Mon, 9 Jun 2014 09:06:27 +0200
Organization: cbb software GmbH
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Date: 2014-06-09T09:06:27+02:00
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On Mon, 09 Jun 2014 08:30:34 +0300, Niklas Holsti wrote:

> On 14-06-08 22:36 , Dmitry A. Kazakov wrote:
>> On Sun, 8 Jun 2014 09:13:11 -0700 (PDT), Dan'l Miller wrote:
>> 
>>> Unfortunately, Ada's downcast syntax is not so obnoxiously conspicuous to
>>> the human eye or to mere regular-expression-only pattern-matchers.
>> 
>> Downcast is not a problem in the given example. The problem is
>> inconsistently implemented multi-method.
> 
> In Georg's example, the methods have a single argument, so it was not a
> mixed multi-method problem. I mentioned the mixed multi-method case as
> an Ada run-time error that is closer to a "missing method" error.

Yes. Your example was correct. I objected to Georg's analysis. Syntax of
downcast is barely related to this. In both cases the language invents a
method (e.g. as raising something), since a call cannot really fail anyway.
The language-invented methods here are unsafe because it is not what the
programmer would normally expect calling them [*]. Thus in both cases the
languages are unsafe.

Ada is obviously safer because the area where the problem arise is much
narrower (only tagged types, only multi-methods, only certain and rare
cases of multi-method calls).

------
*  Robert's definition of unsafety formulated differently: unexpected
behavior from familiar syntax ["misuse"].

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