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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada 202x and square brackets
Date: Wed, 20 Feb 2019 17:47:51 -0600
Organization: JSA Research & Innovation
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Date: 2019-02-20T17:47:51-06:00
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"Lucretia" <laguest9000@googlemail.com> wrote in message 
news:b773bbfa-9fd0-431a-8ff3-462b2c5ccd15@googlegroups.com...
> On Wednesday, 20 February 2019 14:32:14 UTC, Jere  wrote:
>> On Tuesday, February 19, 2019 at 5:01:05 PM UTC-5, Lucretia wrote:
>> > Hi,
>> >
>> > I've noticed whilst looking through the grammar of draft 17 there are a 
>> > lot of new uses of '[' ']' without much explanation. Can someone 
>> > elaborate?
>> >
>> > Ta,
>> > Luke.
>>
>> I know you found it, but for other's benefit, which did you find.  I
>> searched through and found them used in "reduction expressions" [1],
>> but I don't know if that was the only use
>>
>> [1]: http://www.ada-auth.org/standards/2xrm/html/RM-4-5-10.html#I3068
>
> It was aggregates for containers, so you can do Set := [1,2,3,4] or 
> something like that. I didn't read the details.
>
> http://www.ada-auth.org/standards/2xaarm/html/AA-4-3-5.html

You can also use them around array aggregates, so that you can write a 
single component array aggregate:

             My_Arr : constant Some_Unconstrained_Array_Type := [1];

Container aggregates are roughly user-defined array aggrgeates. 
(Alternatively, you can [maybe should] think of an array as a built-in 
container.)

                                  Randy.