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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Overriding Default_Component_Value in derived array type
Date: Tue, 21 Apr 2020 16:32:48 -0500
Organization: JSA Research & Innovation
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Xref: reader01.eternal-september.org comp.lang.ada:58457
Date: 2020-04-21T16:32:48-05:00
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"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
news:hg8rdgFpoa2U1@mid.individual.net...
> I'm seeing behaviour that looks strange to me when I derive an array type 
> from another and use a Default_Component_Value aspect that tries to 
> override the corresponding aspect of the parent type. The parent's default 
> value is used also for the derived type, that is, the aspect definition 
> for the derived type has no effect, it seems.
>
> This is on macOS Mojave (10.14.6), GNAT Community 2019 (20190517-83).
>
> An example:
>
>       type Number is range 1 .. 15;
>
>       type Arr_2 is array (3 .. 5) of Number
>       with Default_Component_Value => 2;
>
>       type Arr_6 is new Arr_2
>       with Default_Component_Value => 6;

This is usually illegal by 13.1(10), so it is very rarely done. (If there 
are any subprograms for Arr_2, then Arr_6 is illegal.) We're talking about 
repealing 13.1(10), which will make it more necessary for compilers to get 
this sort of stuff right.
...
> Bug or feature?

Surely bug. If one didn't give the Default_Component_Value aspect, then of 
course the value would inherit. But be careful that you're not using an 
inherited routine (that would of course use the value for it's own type).

BTW, my understanding is that AdaCore is reworking Default_Value and 
Default_Component_Value because some silly person (that would be me) wrote a 
bunch of ACATS tests for those aspects. (That's why the request came in to 
repeal 13.1(10)). The next version is likely to be better.

                       Randy.