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Date: Thu, 24 Jan 2019 00:06:49 -0800 (PST)
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Subject: Re: Problem with Position of the enumeration Type
From: AdaMagica <christ-usch.grein@t-online.de>
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Xref: reader01.eternal-september.org comp.lang.ada:55356
Date: 2019-01-24T00:06:49-08:00
List-Id: <comp.lang.ada>

Am Mittwoch, 23. Januar 2019 13:08:34 UTC+1 schrieb Luis Ladron de Guevara =
Moreno:
> El mi=C3=A9rcoles, 23 de enero de 2019, 11:33:36 (UTC+1), AdaMagica  escr=
ibi=C3=B3:
> > See RM 13.4(11/3)ff:
> > NOTES
> > 14 Unchecked_Conversion may be used to query the internal codes used fo=
r
> > an enumeration type. The attributes of the type, such as Succ, Pred, an=
d Pos, are unaffected by the enumeration_representation_clauserepresentatio=
n_clause.
> >=20
> > Some questions on your code:
> >=20
> >   Position : Integer;  -- Why is this Integer and not Natural?
> >   =20
> >   for I in E_Test'Base loop  -- Why do you use 'Base here?
>=20
> I wrote a Integer as an example, i could add Natural also, for this examp=
le there are not difference.

It does make a difference. Ada has subtypes just for this purpose: If you k=
now that the values of an object of some type belong only to some subtype, =
you indicate this in the declaration.
This is the very idea of stong typing.

> I'm using 'Range to go through all the positions in enumeration.

No, you used 'Base.

For a enum type E, these are always the same:

for V in E loop
for V in E'Range loop

For an enum type that is not derived, E'Base is the same as E. For types de=
rived from E, there might be a difference.

> I tried to use Ada.Unchecked_Conversion and i got obtain the values for t=
he position. but as you told me, if i use 'post (), the number of the list =
start in 0.

Yes, this is what the RM prescribes.