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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Array index overloading
Date: Thu, 7 Aug 2014 00:17:12 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:21502
Date: 2014-08-07T00:17:12-05:00
List-Id: <comp.lang.ada>

"Peter Chapin" <PChapin@vtc.vsc.edu> wrote in message 
news:ppKdnfmkdIYX-n_ORVn_vwA@giganews.com...
> On 2014-08-06 12:47, marmaduke.woodman@univ-amu.fr wrote:
>
>> Handling index arrays and generating an output array is something I can 
>> write, so my question is if the syntax can be overloaded, or I should 
>> expect to implement an explicit "slice" function?
>
> As Pascal mentioned one dimensional array slices are supported in Ada by
> just indexing using notation A(I .. J) for array A. If you want
> non-unity strides, or multi-dimensional slices, or some other fancier
> effects, you will need to turn to a library of some kind.
>
> Although as I write this I'm wondering if a subtype with a static
> predicate could cover some of those bases. Hmm.

You'll find that it is illegal to declare an array with an index subtype 
that has one or more predicates. We didn't want compilers to have to support 
"holey" arrays or slices.

One could create a container that supported almost any sort of indexing that 
someone wanted. In particular, the Map containers support using the indexed 
notation on the Key_Type, and the Key_Type can be pretty much anything you 
want, so long as it is non-limited.

So, with appropriate declarations, you can write:

     Storage ("Bob") := Obj1;
     Storage ("Randy") := Obj2;
     if Storage ("Tuck") = Storage ("Randy") then ...

and so on.

                              Randy.