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From: Phil Clayton <phil.clayton@lineone.net>
Newsgroups: comp.lang.ada
Subject: Re: initialize an array (1-D) at elaboration using an expression
 based on the index?
Date: Sat, 16 Oct 2010 03:08:49 -0700 (PDT)
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Date: 2010-10-16T03:08:49-07:00
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On Oct 16, 1:16=A0am, Adam Beneschan <a...@irvine.com> wrote:
> On Oct 15, 4:31=A0pm, "Vinzent Hoefler" <nntp-2010...@t-
>
>
>
> domaingrabbing.de> wrote:
> > On Sat, 16 Oct 2010 01:03:52 +0200, Nasser M. Abbasi <n...@12000.org> w=
rote:
>
> > > I was wondering if in Ada I can initialize some array, where I can fi=
ll
> > > the content of each entry in the array based on some function of the =
index?
>
> > Not that I know of.
>
> > At first, you don't have an index at the point of the expression, so
> > you can not parametrize a function with the "current" index returning t=
he
> > appropriate value.
> > At second, if you try to be smart and provide a non-pure function that
> > counts the number of calls to it and provides an appropriate new return
> > value on each call, this is not guaranteed to work, because the evaluat=
ion
> > order is "arbitrary".
>
> > Still, you can use an array aggregate like:
>
> > a: array(1..N) of float :=3D (1 =3D> Eval (1), 2 =3D> Eval (2), ...);
>
> > but I wouldn't recommend that due to its lack of flexibility if the
> > index constraint changes.
>
> > Vinzent.
>
> It seems like it would be simple to add syntax to array aggregates in
> the language like
>
> a : array(1..N) of Float :=3D (for I in 1..N =3D> Float(I)*Float(I));
>
> The legality rules and rules about applicable index constraints would
> be the same as if "for I in" were not present.
>
> Perhaps someone has already made a similar proposal, but I can't find
> it. ...

There was a recent discussion about exactly this on c.l.a. that
spawned off a thread on conditional expressions:

http://groups.google.com/group/comp.lang.ada/browse_thread/thread/334f90127=
42e58fc/bc4410d521cd9e9c#bc4410d521cd9e9c

Phil