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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: null range from 1 element discrete type
Date: 1999/11/22
Message-ID: <wcciu2uxy1i.fsf@world.std.com>#1/1
X-Deja-AN: 551685366
Sender: bobduff@world.std.com (Robert A Duff)
References: <v03020900b45ad0cb9379F@[192.54.146.15]>
 <3835D5A0.F906D31D@mitre.org>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1999-11-22T00:00:00+00:00
List-Id: <comp.lang.ada>

"Robert I. Eachus" <eachus@mitre.org> writes:

>     Technically there is no "perfect" solution, as the compiler is
> allowed to choose a size of zero bits for such a type.  

The compiler is *required* to choose 'Size = 0, and of course that's the
natural thing for the compiler to do -- anything else would require a
special case in the compiler.

But I don't see what 'Size has to do with the issue.

>...But if the
> (sub)type is a generic formal type, you shouldn't have to worry about
> this possibility.
> 
>     Since you always want a null range try:  T'Val(1) .. T'Val(0)  Since
> 'Val returns the base type of T, as long as the base type of T contains
> at least one bit you are safe.

T'Val(1) will raise Constraint_Error if T is an enum type with only one
value.  The number of bits allocated for objects of type T has nothing
to do with this.

- Bob