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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Using the GNAT defined attribute: 'Enum_Rep
Date: 1997/09/08
Message-ID: <EG7Enp.3DF@world.std.com>#1/1
X-Deja-AN: 270772351
References: <97082719523509@psavax.pwfl.com>
 <340D6C5D.2E53@pseserv3.fw.hac.com>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1997-09-08T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <340D6C5D.2E53@pseserv3.fw.hac.com>,
W. Wesley Groleau x4923 <wwgrol@pseserv3.fw.hac.com> wrote:
>...  And in Ada 83, the above 
>would not be legal because 'Size is _defined_ as non-static, thus 
>can't be used to specify another 'Size.

S'Size is static if S is a static subtype (in both Ada 83 and 95).

>>      'Pos and 'Val. ... will work If and only if the representation is
>>     identical to the position numbers - what you get if you don't
>>     specify a representation. ....
>
>Is this true ?

Yes.

>...  Seems to me it's legal (though I've never seen
>it happen) for an implementation to generate anything it wanted
>for a representation as long as ordering, indexing, etc. worked.

Yes, but 'Pos and 'Val still need to return what the RM says, which is
*not* based on the representation.

>I can imagine a CPU where a bit per value is more efficient, i.e., 
>an implicit
>
>   for Enum use ( 0, 1, 2, 4, 8, 16, 32, ... );

Fine, but the 'Pos values are still 0, 1, 2, 3, ...

>though, again, I've never seen that done.

Me neither.  We probably never will, either.

- Bob