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From: Petter <petter_fryklund@hotmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Rep Specing Variant Records
Date: Wed, 16 Sep 2009 01:19:54 -0700 (PDT)
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Date: 2009-09-16T01:19:54-07:00
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Yes, discriminants do take up size.

This is how I would do it:

type Stuff (Has_Extra : Boolean) is record
 =A0 =A0 Foo : Integer;
 =A0 =A0 Bar : Integer;
 =A0 =A0 case Has_Extra is
 =A0 =A0 =A0 =A0 when True =3D>
 =A0 =A0 =A0 =A0 =A0 =A0 Blah : Float;
 =A0 =A0 =A0 =A0 when False =3D>
 =A0 =A0 =A0 =A0 =A0 =A0 null;
 =A0 =A0 end case;
 end record;

 for Stuff use record
     Has_Extra at  0 range 0 .. 31;
 =A0 =A0 Foo       at  4 range 0 .. 31;
 =A0 =A0 Bar       at  8 range 0 .. 31;
     Blah      at 12 range 0 .. 31;
 end record;

type Other_Stuff (Has_Blah : Boolean) is record
     Foo : Integer;
     Bar : Integer;
     case Has_Blah is
         when True =3D>
             Blah : Float;
         when False =3D>
             Blip : Integer;
     end case;
 end record;

 for Other_Stuff use record
     Has_Blah  at  0 range 0 .. 31;
     Foo       at  4 range 0 .. 31;
     Bar       at  8 range 0 .. 31;
     Blah      at 12 range 0 .. 31;
     Blip      at 12 range 0 .. 31;
 end record;