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Newsgroups: comp.lang.ada
Date: Mon, 18 Jun 2018 14:27:11 -0700 (PDT)
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Subject: Re: Ada Successor Language
From: ric.wai88@gmail.com
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Xref: reader02.eternal-september.org comp.lang.ada:53147
Date: 2018-06-18T14:27:11-07:00
List-Id: <comp.lang.ada>

On Monday, June 18, 2018 at 5:20:32 PM UTC-4, Shark8 wrote:

> I'd honestly like the ability to use X'Type; this would allow us to say s=
omething like this:
>=20
> Procedure Swap( A, B : in out Some_Type ) is
>   Temp : Constant B'Type :=3D B;
> Begin
>   B:=3D A;
>   A:=3D Temp;
> End Swap;
>=20
> Yeah, I know, it's a little thing and you can do it with generics, etc. B=
ut that's not entirely the point, the point is that this allows the declara=
tion of types dependent on objects... it provides some of the niceties of t=
ype-inference without having to resort to such lazy/possibly-error-prone me=
thodologies.


Why would you want that? You have to have visibility to the type to declare=
 an object of the type. In your above example, you explicitly know about So=
me_Type, and you also explicitly know that A and B are of that type. So you=
 don't need to query the parameter, since it is implicit.

Your example above has no purpose. It would be better in ever single respec=
t to just say:

Temp: constant Some_Type :=3D B;

Any other case where you wouldn't know about the type until runtime is exac=
tly what generics are for.