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Date: Fri, 04 May 2012 12:37:01 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Newsgroups: comp.lang.ada
Subject: Re: OOP in Ada: Alternatives for "protected" scope
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Date: 2012-05-04T12:36:59+02:00
List-Id: <comp.lang.ada>

On 03.05.12 23:27, Felix Krause wrote:
> Now there is some calculation to be done while execution Do_Something which cannot be defined in A.
> (...)
> In languages like Java and C#, there is a "protected" scope to cope with this situation.

There are some O-O solutions.

One solution is outlined by at least on Java guru, and by the Objective-C
programming model in ***step.  In short, replace procedural style
with O-O style (sounds odd, but that's really what it does;
the dependence of A/Do_Something on Calculate is an implicit
procedural thing).

with Calculators;
package P_A is

    type A is abstract tagged private;

    procedure Do_Something (Object : in out A);


    --
    -- Add your type of computation here to be performed
    -- at some time during the execution of Do_Something:
    --
    procedure Link
        (Object : in out A;
         Computation: Calculators.Calculator'Class);

private

    type Circuits is
        access constant Calculators.Calculator'Class;

    type A is abstract tagged record
       Machine : Circuits;
    end record;

end P_A;

If necessary things can be moved further down the package and/or
type hierarchy if the presence of a calculation should be hidden
at the top level.