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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.ada
Subject: Re: Problem with Position of the enumeration Type
Date: Wed, 23 Jan 2019 15:47:05 -0800
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Date: 2019-01-23T15:47:05-08:00
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"Randy Brukardt" <randy@rrsoftware.com> writes:
> "Simon Wright" <simon@pushface.org> wrote in message 
> news:lyzhrruww2.fsf@pushface.org...
> ...
>> As Karl Müller <mtb23@gmx.de> hinted, you can use the non-standard GNAT
>> implementation-defined attribute 'Enum_Rep[1]. The next page describes
>> 'Enum_Val.
>
> It's Standard, just not until Ada 2020. See 
> http://www.ada-auth.org/standards/2xrm/html/RM-13-4.html#p10.1.
>
> (Yes, borrowed from GNAT.)

I'm glad to see this being standardized.

Unchecked_Conversion can be a workaround, but it's difficult
(perhaps impossible) to portably determine the integer type to
which you need to convert.

For example, both of these are valid:

    type Unsigned_Byte is (UMin, UMax);
    for Unsigned_Byte use (0, 255);
    for Unsigned_Byte'Size use 8;

    type Signed_Byte is (SMin, SMax);
    for Signed_Byte use (-128, 127);
    for Signed_Byte'Size use 8;

Both types will have the same representation for the min and max values.
How can you *portably* determine the appropriate target type for an
Unchecked_Conversion that yields the correct values?

(You can do it manually on a case by case basis.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */