From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.9 required=5.0 tests=BAYES_00,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,69d0258abc166f15,start
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!postnews.google.com!f14g2000cwb.googlegroups.com!not-for-mail
From: "Brian" <brian.ngc@gmail.com>
Newsgroups: comp.lang.ada
Subject: GNAT Unchecked_Union and multiple components
Date: 18 Apr 2005 07:58:00 -0700
Organization: http://groups.google.com
Message-ID: <1113836280.439166.180090@f14g2000cwb.googlegroups.com>
NNTP-Posting-Host: 208.20.220.72
Mime-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
X-Trace: posting.google.com 1113836285 14483 127.0.0.1 (18 Apr 2005 14:58:05
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Mon, 18 Apr 2005 14:58:05 +0000 (UTC)
User-Agent: G2/0.2
Complaints-To: groups-abuse@google.com
Injection-Info: f14g2000cwb.googlegroups.com; posting-host=208.20.220.72;
   posting-account=YwIosQ0AAAAoDcE7AKA726BVRd2vd_jK
Xref: g2news1.google.com comp.lang.ada:10526
Date: 2005-04-18T07:58:00-07:00
List-Id: <comp.lang.ada>

Hi,

I've started to use GNAT 3.15p and noticed it handles the pragma
Unchecked_Union differently from other compilers.  According to the
GNAT Reference Manual "Each variant has a component list with a single
component.", if you violate this rule the compiler will generate the
error "Unchecked_Union variant can have only one component".  Other
compilers allow multiple components per variant.  Is there a GNAT
compiler switch I can use to loosen this restriction?  My current
workaround is to create a new record type containing the multiple
components and use it as the type for one of the variants (see code
snippet below).  Thanks.

Regards,
Brian


<snip>

type Msg_Type is (Msg_A, Msg_B);

-- This is what I want as my variant record type definition.

type Data_Type1(Msg : Msg_Type := Msg_A) is
   record
      case Msg is
         when Msg_A =>
            A1 : Integer;
            A2 : Integer;
         when Msg_B =>
            B : Float;
      end case;
   end record;

-- This is my current workaround.

type Msg_A_Variant is
   record
      A1 : Integer;
      A2 : Integer;
   end record;

type Data_Type1(Msg : Msg_Type := Msg_A) is
   record
      case Msg is
         when Msg_A =>
            A : Msg_A_Variant;
         when Msg_B =>
            B : Float;
      end case;
   end record;

-- end workaround

pragma Unchecked_Union(Data_Type1);

<snip>