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From: Vinzent Hoefler <JeLlyFish.software@gmx.net>
Newsgroups: comp.lang.ada
Subject: Re: Test for > 'last
Date: Fri, 14 Mar 2003 13:10:58 -0500
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Date: 2003-03-14T13:10:58-05:00
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"Ant" <ant@work.invalid> wrote:

>"Peter Richtmyer" <prichtmyer@yahoo.com> wrote in message
>news:1b585154.0303140406.124c3312@posting.google.com...
>> This may be trivial, but I have come across some code
>> in a (weapon control) system that does checks similar
>> to:
>>
>>     ---------------------------------------
>>     if enum_input < enum_type'first or
>>        enum_input > enum_type'last then
>>        -- handle the input error
>>     ---------------------------------------
>
>[...]
>
>> But I am wondering whether people think the original code
>> is OK, sort of wrong, really grossly wrong, or what.
>
>I would rather do this:
>
>if enum_input not in enum_type'first .. enum_type'last then
>  -- handle error
>end if;

And would be wrong, too, if enum_input also has the type enum_type.

If you look closer to this, this statement does not make sense and the
compiler is indeed not required to check this, because the contract
tells him, this condition will *always* be false (even if in fact it
might not be). What else should a enum_input contain than some value
of enum_type?

Either use 'Valid or use a type that is allowed to contain values
outside the range of the type to be compared with.


Vinzent.