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From: "G.B." <bauhaus@notmyhomepage.invalid>
Newsgroups: comp.lang.ada
Subject: Re: A function that cannot be called?
Date: Thu, 18 Oct 2018 21:36:00 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:54635
Date: 2018-10-18T21:36:00+02:00
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On 18.10.18 19:03, AdaMagica wrote:
> Am Donnerstag, 18. Oktober 2018 14:14:32 UTC+2 schrieb G.B.:
>> package What is
>>
>>       type Void (<>) is private;
>>
>>       function Impossible (X : T) return Void;
>>
>> private
> ...
>> end What;
> 
> Of course this is possible. Declarations of objects of type Void must have an initial value, which can be provided via the "constructor" Impossible:
> 
> X: Void := Impossible (T0);

Impossible needs to return a value. But a returned object can
neither be declared nor a value constructed, since type Void
has an unknown discriminant so that no initial constraint
can be given anywhere.