Re: initialize an array (1-D) at elaboration using an expression based on the index?

[Adam Beneschan <adam@irvine.com>]

On Oct 15, 4:31 pm, "Vinzent Hoefler" <nntp-2010...@t-
domaingrabbing.de> wrote:
> On Sat, 16 Oct 2010 01:03:52 +0200, Nasser M. Abbasi <n...@12000.org> wrote:
>
> > I was wondering if in Ada I can initialize some array, where I can fill
> > 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 the
> 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 evaluation
> order is "arbitrary".
>
> Still, you can use an array aggregate like:
>
> a: array(1..N) of float := (1 => Eval (1), 2 => 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 := (for I in 1..N => 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.  Since Ada 2012 is already putting "if" and "case" in expressions,
though, it shouldn't be too big a leap to include "for" in an
expression.  Of course, it's too late to make it into Ada 2012, but
perhaps I'll propose it for the next version of Ada (what is that
going to be?  Ada 2020, where we add all the features that we realize
in hindsight that we should have added earlier? :-)).

                                       -- Adam