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From: Shark8 <onewingedshark@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: OOP in Ada: Alternatives for "protected" scope
Date: Fri, 4 May 2012 21:33:59 -0700 (PDT)
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Date: 2012-05-04T21:33:59-07:00
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On Friday, May 4, 2012 1:48:53 PM UTC-5, Felix Krause wrote:
>Compared to my version (with redispatching issues fixed), this
alternative enforces a weaker contract. It does not enforce the child
classes to call Do_Prologue and Do_Epilogue when implementing
Do_Something. While this fixes the problem that I cannot have an
abstract method in the private part, I think the mix-in solution you
suggested in your second post is a better way to handle this.


Couldn't you fix this by something like the following:

Type Base is tagged null record;

Procedure Do_Prolog( Object : in out Base'Class );
Procedure Do_Epilog( Object : in out Base'Class );
-- Both called defined in the body

Procedure Work( Object : in out Base ) is abstract;
Procedure Do_Work( Object : in out Base'Class );

with a body of:
Procedure Do_Work( Object : in out Base'Class ) is
begin
  Object.Do_Prolog;
  Object.Work;
  Object.Do_Epilog;
end Do_Work;

Or am I misunderstanding your intent?