Re: A question re meaning/use of the "for ... use ..."

From: "David C. Hoos" <david.c.hoos.sr@ada95.com>
To: "Keith Thompson" <kst-u@mib.org>
Cc: "comp.lang.ada@ada.eu.org" <comp.lang.ada@ada-france.org>
Subject: Re: A question re meaning/use of the "for ... use ..."
Date: Wed, 8 Dec 2004 07:48:06 -0600
Date: 2004-12-08T07:48:06-06:00	[thread overview]
Message-ID: <mailman.179.1102513844.10401.comp.lang.ada@ada-france.org> (raw)
In-Reply-To: ln8y8932ei.fsf@nuthaus.mib.org

The Unchecked_Conversion is not between the 'Pos attribute and
the representation, but rather between the enumeration type and its
representation.

All that is necessary for portability is to constrain the 'Size of both
the enumeration type, and the integer type of its representation to
have identical sizes.

----- Original Message ----- 
From: "Keith Thompson" <kst-u@mib.org>
Newsgroups: comp.lang.ada
To: <comp.lang.ada@ada-france.org>
Sent: Tuesday, December 07, 2004 9:18 PM
Subject: Re: A question re meaning/use of the "for ... use ..."

> "Randy Brukardt" <randy@rrsoftware.com> writes:
> > "Jeffrey Carter" <spam@spam.com> wrote in message
> > news:H1Hsd.1987$yr1.256@newsread3.news.pas.earthlink.net...
> >> Stephen Leake wrote:
> >>
> >> > There is no standard attribute that returns the internal
> >> > representation specified by the enumeration representation clause.
> >> > However, GNAT provides the non-standard 'Enum_Rep for this purpose.
> >>
> >> I have no problem with 'Pos returning the abstract position number, but
> >> do think something like GNAT's 'Enum_Rep should be standard, along with
> >> a conversion the other way, equivalent to 'Val ('Enum_Val?).
> >
> > The ARG discussed this long ago, and concluded that such a facility
isn't
> > needed. That's because Unchecked_Conversion provides the needed support.
> > Indeed, this is one of the few cases where the result of
> > Unchecked_Conversion is defined by the language (using it in this way
will
> > work on all Ada compilers). There was some discussion about syntax
guides
> > that prohibit the use of Unchecked_Conversion, but there is a lot of
> > discomfort about changing the language just because some people's style
> > guides are broken...
>
> How do you portably choose the target type for the Unchecked_Conversion?
>
> The 'Pos attribute returns a result of type universal_integer; there's
> no way to make an Unchecked_Conversion return a universal_integer.
>
> -- 
> Keith Thompson (The_Other_Keith) kst-u@mib.org
<http://www.ghoti.net/~kst>
> San Diego Supercomputer Center             <*>
<http://users.sdsc.edu/~kst>
> We must do something.  This is something.  Therefore, we must do this.
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