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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Extending a type and Finalization
Date: Fri, 5 Jun 2009 05:21:28 -0700 (PDT)
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Date: 2009-06-05T05:21:28-07:00
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Pascal Malaise wrote on comp.lang.ada:
> I declare P.T as "new Ada.Finalization.Controlled with record ..." and
> I don't define Finalize for it.
> Then in Pp I declare Tt as "new P.T with record ..." and I declare an
> overriding procedure Finalize (V : in out Tt) and its body in Pp body.
> It does not compile, with error: 'subprogram "Finalize" is not
> overriding'
>
> Same if I define in P a Finalize for T.
>
> Any idea?
>
> ------------------------------
> with Ada.Finalization;
> package P is
> =A0 type T is tagged private;
> private
> =A0 type T is new Ada.Finalization.Controlled with record
> =A0 =A0 I : Integer;
> =A0 end record;
> end P;
>
> with P;
> package Pp is
> =A0 type Tt is tagged private;
> private
> =A0 type Tt is new P.T with record
> =A0 =A0 Ii : Integer;
> =A0 end record;
> =A0 overriding procedure Finalize (V : in out Tt);
> end Pp;
>
> package body Pp is
> =A0 overriding procedure Finalize (V : in out Tt) is
> =A0 begin
> =A0 =A0 null;
> =A0 end Finalize;
> end Pp;

That's because P.T is a *private* record extension of
Ada.Finalization.Controlled. Package PP cannot see that P.T derives
from it.

Solution 1: rename PP to P.P, a child package of P so it can see the
private part of P.

Solution 2: make P.T a public record extension:

type T is new Ada.Finalization.Controlled with private;

But I recommend that you *not* derive P.T from any other type; use a
mixin instead. Making a type controlled is not a good enough reason
for making it tagged.

--
Ludovic Brenta.