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From: dmitry@elros.cbb-automation.de (Dmitry Kazakov)
Newsgroups: comp.lang.ada
Subject: Re: Ada The Best Language?
Date: Mon, 23 Jul 2001 11:51:53 GMT
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Date: 2001-07-23T11:51:53+00:00
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On Mon, 23 Jul 2001 10:27:27 +0200, "Bertrand Augereau"
<baugereau@ifrance.kom> wrote:

>> enum COLOR { BLUE, RED, GREEN };
>>
>> int main (void)
>> {
>>    COLOR X = BLUE;
>>
>>    switch (X)
>>    {
>>        case 0   : break;
>>    }
>>    return 0;
>> }
>
>I don't see this type of code as a coding mistake, it is just a nonsense way
>of doing it. This can only be an intentional mistake and type safety is
>there mainly for protecting you against non-intentional mistakes.

What is the difference between "intentional" and "non-intentional"
mistakes? Both result in blue-screen. It is nice to have Windows. We
can always say, that it is Microsoft's fault when our programs crash
(:-)). But what would be a blue-screen for a flight control system?

>That's what forbidding implicit int->enum is for.

Does the code above not contain an implicit int->enum conversion? 

>I'm not sure a compiler has to take care of this error, though Ada
>programmers might think otherwise.

No doubts. BTW in Ada the counterpart of C++ switch statement shall
cover all alternatives, so being translated into Ada

switch (X)
{
   case BLUE  : break;
}

would be also illegal, because it is not clear what to do with RED and
GREEN.

>It is often nice to have a enum->int conversion, especially when you can map
>your enum to some int you need.
>
>enum BOOL {
>    FALSE = 0,
>    TRUE = !0;
>};
>
>Then if you need a enum->int mapping, you just have it for free by the fact
>enum are reprensented by int in the machine (as with Ada, I suppose). I
>think you can do that in Ada if you need it with using clause.

enum <-> int mapping is an implementation detail. There is no need to
expose it. A program that relies on the fact that on some particular
machine, occasionaly the representation of COLOR::BLUE and int::0 are
same, is poorly designed. That C++ allows such things be implicit [in
Ada you may achieve the same effect only by an explicit way], is a
clear language design fault.

Regards,
Dmitry Kazakov