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From: Maciej Sobczak <see.my.homepage@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Enforcing initialization protocol for protected type
Date: Mon, 7 Sep 2009 13:19:02 -0700 (PDT)
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Date: 2009-09-07T13:19:02-07:00
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On 7 Wrz, 19:01, Georg Bauhaus <rm.dash-bauh...@futureapps.de> wrote:

> The following is not using, I guess, your original
> idea directly. =A0But it requires that the a proper context
> be set up. =A0Then, the PO will initialize itself from
> the context. =A0Context is passed in via known discriminants:
[...]

I see. I guess that in addition to passing the factory (function on
object, as in your example), the state itself can be passed via
discriminant as well.
This would leave the factory call at the user side (note that in your
example it was the protected object itself that called the factory),
which would give more control on factory call parameters and such.

type State is private;
type State_Ptr is access State;

function Make_PO return State_Ptr;
function Make_PO (Some : T; Parameters : T) return State_Ptr;
-- ...

protected type PO (S : State_Ptr) is
-- ...
private
    St : State_Ptr :=3D S;
end PO;

so that the typical creation pattern would be:

X : PO (Make_PO);
Y : PO (Make_PO (ABC, DEF));

This, however, opens another question: controlled finalization of
protected types to release the state object, if it was allocated
dynamically. Oops.
But a controlled component of the protected type can take care of
that.
Does it make sense?

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com

Database Access Library for Ada: www.inspirel.com/soci-ada