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Newsgroups: comp.lang.ada
Date: Wed, 30 Jul 2014 18:29:10 -0700 (PDT)
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Subject: Re: Quick question regarding limited type return syntax
From: Adam Beneschan <adambeneschan@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:21363
Date: 2014-07-30T18:29:10-07:00
List-Id: <comp.lang.ada>

On Wednesday, July 30, 2014 6:00:43 PM UTC-7, NiGHTS wrote:
> On Wednesday, July 30, 2014 8:48:34 PM UTC-4, Shark8 wrote:
>=20
> > On 30-Jul-14 17:51, NiGHTS wrote:
>=20
> > >   return  Object (Connection_String'Access) do null; end return;

> package body Test is
>    function Create(...) return Object is
>       ...
>    begin
>       return Object'(Connection_String'Access);
>    end;
>    ...
> end Test;

What you need to do is return an aggregate.  And to return an aggregate, yo=
u need to specify both fields--the Parameters discriminant and the Database=
.  This syntax:

    Object'(Connection_String'Access)

is just wrong.  It tells the compiler that the value is Connection_String'A=
ccess, and asks the compiler to treat it as an Object.  It can't do that, b=
ecause Object isn't an access type.  (This sort of syntax can be useful in =
overloading cases, when the compiler can't determine the correct access typ=
e without help.)

If you said

    Object'(Parameters =3D> Connection_String'Access)

you'd get an error that Database is missing.  So you need

    Object'(Parameters =3D> Connection_String'Access, Database =3D> <>)

or just

    (Parameters =3D> Connection_String'Access, Database =3D> <>)

or   =20

    (Parameters =3D> Connection_String'Access, others =3D> <>)

(It's OK for a function that returns a limited type to return an aggregate =
like this.)

The effect is that subcomponents of Database that have default initial valu=
es will be initialized, and subcomponents that don't have default initial v=
alues will be initialized to garbage (except where the language says otherw=
ise).  That's really the same as your original example was trying to do.  I=
 guess that explicitly putting "others =3D> <>" in an aggregate is enough t=
o convince GNAT not to think you were accidentally leaving something initia=
lized to garbage. =20

                              -- Adam