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From: "G.B." <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Uninitialized out parameters.
Date: Wed, 6 Apr 2016 12:17:05 +0200
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Date: 2016-04-06T12:17:05+02:00
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On 06.04.16 10:19, ahlan@marriott.org wrote:
> On Tuesday, April 5, 2016 at 6:19:47 PM UTC+2, G.B. wrote:
>> On 05.04.16 14:02, ahlan@marriott.org wrote:
>>>     Ada.Text_IO.Put_Line ("V:" & V'img);
>>>
>>> The value zero is output, which because V is positive should be impossible.
>>
>> Addressing just this issue: the line is calling
>> implementation defined attribute 'IMG, which can
>> do as it pleases. The Ada type attribute 'Image
>> takes a value of type Positive'Base, which includes 0,
>> which is why outputting 0 is perfectly fine.
>>
>> (It's not a subtype attribute, but a type attribute,
>> if this makes sense.)
>
> The issue here is not whether or not 'img fails but the fact that V is returned with a value out of range.

The issue is rather, I think, whether V is returned at all.
There would have to be an assignment within the null procedure.

> But even that is not the point I'm trying to make.
> I am suggesting that it ought not to be possible to define a null procedure that has out parameters without some form of warning being issued.

I think the usual answer is that the compiler is not a mind
reader and the best you could get is a warning. Who knows?
Maybe the technical requirements are such that the programmer
uses a procedure like Test as a placeholder, maybe its existence
is dictated by an abstract type, maybe a null procedure really
should do nothing at all, which includes not touching V.