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From: "Ekkehard Morgenstern" <ekkehard.morgenstern@onlinehome.de>
Newsgroups: comp.lang.ada
Subject: Re: Problem with protected type
Date: Tue, 25 Nov 2003 19:39:48 +0100
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"Robert I. Eachus" <rieachus@comcast.net> schrieb im Newsbeitrag
news:Kp6dnRXjpqyY416iRVn-sw@comcast.com...
> > But why is this necessary?
>
> It isn't in general.  What you are missing is a complete definition of
> CoreEvent before you try to create an object of the type:
>
>    EventObject : CoreEvent;  <----

Thanks. I didn't realize was creating an object named BaseEvent, I omitted
the "type" keyword.


> Replacing EventObject by a pointer to CoreEvent eliminates the need for
> "knowing" the size of CoreEvent.  Other fixes would be to complete the
> declaration of CoreEvent before the declaration of BaseEvent,

How could I declare the CoreEvent record layout as private without putting
the declaration in the private section?

>  or to make
>   BaseEvent a protected type, then not create any objects of the type in
> the public part of the package specification.  (You may want to create
> such objects in child packages.)

That's true, I wanted to declare a type, not an object. ;-)

> I would think that the intent is to have several objects of type
> BaseEvent, so the latter would be the best fix.

Yes!

> This principle of linear elaboration order is followed thoughout Ada.
> There are cases where it is a pain, and other cases where it has
> benefits.  But there needs to be one rule for such things, and this rule
> was chosen as the simplest for users to understand.

Ok.

> Incidently, there is no language rule against the style of identifier
> you are using, but Ada compilers and editors do a better job of
> supporting Base_Event instead of BaseEvent.  For example the emacs
> ada-mode I use automatically converts BaseEvent to Baseevent unless I go
> to extra effort.

Thanks. I didn't know that! :-)