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Newsgroups: comp.lang.ada
Subject: Re: Constant record components
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From: M E Leypold
 <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>
Date: 04 Jul 2006 02:08:38 +0200
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"ME" <abcdefg@nonodock.net> writes:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:t7hmlpeqyass.1fjxzy2pl8z82$.dlg@40tude.net...
> > On Sun, 2 Jul 2006 09:13:54 -0700, ME wrote:
> >
> >> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> >> news:1loq7utmaxvll$.yqsxj5edzqgv.dlg@40tude.net...
> >>> On Sat, 1 Jul 2006 09:25:06 -0700, ME wrote:
> >>>
> >>>> What was the rationale for prohibiting constant record components?
> >>>
> >>> Initialization and composition issues. Then often it is argued that
> >>> discriminants are, though limited.
> >
> >> What were these issues?
> >
> > You should ask language lawyers. Consider aggregates:
> >
> > type Semimutable is record
> >   A : constant Integer := 10;
> >   B : Integer;
> > end record;
> >
> > X : Semimutable := (A => 20, B => 40); -- Constraint_Error?
> > Y : Semimutable := (A => 10, B => 40);
> >
> > It might become tricky when A is a composite or private type. Should it
> > finalize the component and initialize it *same*? In which sense same? Does
> > it skip A upon assignments?

> Yes, why not. Anyway , discriminants allow a type of constant component so 
> the mechanism is possible.

If constant record fields are needed, wouldn't it be simpler to just
wrap the whole initializing and assigning into a functional interface?
It would als help to isolate effects of changes if you switch
representation.

Regards -- Markus