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Date: Fri, 10 Aug 2018 10:04:06 -0700 (PDT)
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Subject: Re: SI Units Checked and Unchecked
From: "Dan'l Miller" <optikos@verizon.net>
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Xref: reader02.eternal-september.org comp.lang.ada:54129
Date: 2018-08-10T10:04:06-07:00
List-Id: <comp.lang.ada>

On Friday, August 10, 2018 at 9:50:53 AM UTC-5, Dmitry A. Kazakov wrote:
> On 2018-08-10 15:59, Dan'l Miller wrote:
> > On Friday, August 10, 2018 at 1:45:47 AM UTC-5, Dmitry A. Kazakov wrote=
:
> >> On 2018-08-10 00:12, Dan'l Miller wrote:
> >>
> >>> Actually, I am talking about compile-time checks within Ada source co=
de for a gauge as would be
> >>> utilized on the GUI control screen of a chemical plant or a nuclear r=
eactor, not some toy string
> >>> processing app that is the analogue of GNU Units.
> >>
> >> As I explained this design is technically not viable.
> >=20
> > in today's Ada.
>=20
> =E2=80=A6 Either way, classes of dimensioned object built as subtypes=20
> with the unit being a constraint or as related types with the unit being=
=20
> the type tag, most designs will use subtype- or class-wide objects.
>=20
> We need a type system capable of static checks when constraints or tags=
=20
> are statically known, a way to convert "Unit_Error may be raised" into=20
> hard type error.

Well, now there is something that we can agree on.

> Then we will have both static checks and zero run-time overhead in=20
> static cases and fallback to dynamic checks in class-wide cases.

I take it =E2=80=A6

> In any Ada.

=E2=80=A6 that you don't think that =E2=80=9CThen we =E2=80=A6 class-wide c=
ases=E2=80=9D sentence is achievable at all in any derivative of Ada due to=
 some fundamental flaw in Ada, and that a significantly not-Ada language is=
 the only hope of achieving that sentence.  Why so?