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Newsgroups: comp.lang.ada
Date: Wed, 30 Jul 2014 17:02:59 -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:21358
Date: 2014-07-30T17:02:59-07:00
List-Id: <comp.lang.ada>

On Wednesday, July 30, 2014 4:51:10 PM UTC-7, NiGHTS wrote:
> I am designing a package which features a "Create" function that returns =
a newly instantiated "Object" which is a discriminated limited type. The co=
de compiles and operates correctly but gives me a warning that "New_Object"=
 is not used. See below (ellipses represent omitted code):

> package Test is
>    type Object (Parameters : access String) is tagged limited private;
>    function Create (...) return Object;
>    ...
> private
>    type Object (Parameters : access String) is tagged limited
>    record
>       Database : PQ.Database (Parameters);
>       ...
>    end record;
>    ...
> end Test;
>=20
> package body Test is
>    function Create(...) return Object is
>       ...
>    begin
>       return New_Object : Object (Connection_String'Access) do=20
>          null;
>       end return;
>    end;
>    ...
> end Test;

> To remove this warning I've tried this:
>=20
>    return  Object (Connection_String'Access) do null; end return;
>=20
> and it gives an error about expecting a ';'. I've also tried this:
>=20
>=20
>=20
>    return  Object (Connection_String'Access);
>=20
> Compiler tells me "argument of conversion cannot be access".=20
>=20
> I have tried other syntax variants but all produce errors. My goal here i=
s to avoid using "new" which is why I am trying to return the instance in t=
his way.
>=20
> How can I rewrite this code so that I won't get any errors or warnings?

What is a PQ.Database? =20

I've tried this with various dummy types for the Database, and when I get a=
 warning it's that the object is "read but never assigned".  Is that the wa=
rning you're getting?  That's different from a warning that says it's never=
 used.

It appears to me that if this field were assigned in New_Object, or if Data=
base had an initial value in the record or if all components of Database ha=
d initial values, you wouldn't get the warning.

                              -- Adam