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Newsgroups: comp.lang.ada
Subject: Re: Correct use of variants
References: <dknag1$2u3$1@sunnews.cern.ch>
From: Stephen Leake <stephen_leake@acm.org>
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Date: Mon, 07 Nov 2005 18:40:54 -0500
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Date: 2005-11-07T18:40:54-05:00
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Maciej Sobczak <no.spam@no.spam.com> writes:

> What is the correct way to achieve the declaration of A with the
> possibility of changing the discriminant later? One of the ways is to
> use *some* default value for the discriminant, 

That is the only way.

> but I might have difficulty deciding which value is better than the
> others for this role. 

It makes absolutely no difference. The syntax makes it look like you
are giving a default value to the discriminant, but it doesn't matter
what value you put; it will never be used.

> An arbitrary choice would create a misleading message to the reader
> that the particular value is considered to be "best" or "idle" or
> "starting" or whatever. 

I usually use:

type Foo_Type (descrim : Descrim_Type := Descrim_Type'first) is ...;

to indicate that I don't care what the default descriminant is.

> In addition, having a default value for the discriminant means that
> it's not obligatory to initialize the variable A while it's declared
> and I would like to keep this enforced.

Other posts have addressed this.

-- 
-- Stephe