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Newsgroups: comp.lang.ada
Date: Sun, 3 Jan 2016 13:21:52 -0800 (PST)
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Subject: Re: Instantiating package problems
From: Andrew Shvets <andrew.shvets@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:29000
Date: 2016-01-03T13:21:52-08:00
List-Id: <comp.lang.ada>

Ok, so basically, my way of thinking about OOP in Ada is flawed.  All packa=
ges, by default, are static (as well as their methods), but if I want to ca=
ll a method (procedure/function) I would have to do this on a type that's i=
nside of a package, yes?

On Sunday, January 3, 2016 at 3:27:29 PM UTC-5, Georg Bauhaus wrote:
> On 03.01.16 19:40, Andrew Shvets wrote:
> > Hi all,
> >
> > This is coming from the perspective of someone that has far more C++ OO=
P experience.  Basically, what I'm trying to do is create an instance of a =
package and then call a function from that object.  This is what I have bel=
ow.  The calculator package is a simple package with the Addition function =
(which, you guessed it, just adds numbers together) that takes two integers=
 and returns an integer.
>=20
> The C++ equivalent of a generic package of Ada would be
>=20
> (a) a generic namespace (with an optional block of statements
> that are executed when the namespace is elaborated), or
>=20
> (b) a generic file that has, alongside any definitions, also said block
> of statements.
>=20
> C++ is different from Ada in this regard, since it has generic types
> only and none of the above, except for preprocessor tricks.
> Ada, OTOH, does not have generic types, only generic units (possibly
> containing types) such as packages and subprograms.
>=20
> "Calculator" of your example names a package, but not a (sub)type,
> this is what the compiler says in its first message.
>=20
> If it is a generic package, then you'd be instantiating packages
> from it, but not objects. Again, unlike C++, which provides for
> some automatically inferred instantiations, Ada requires that
> generic units be instantiated explicitly.
>=20
> > OUTPUT:$ gnatmake -g main.adb calculator.adb
> > gcc -c -g main.adb
> > main.adb:10:10: subtype mark required in this context
> > main.adb:10:10: found "calculator" declared at calculator.ads:5
> > main.adb:22:60: invalid prefix in selected component "Calc"
> > gnatmake: "main.adb" compilation error
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >