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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Allocators and exceptions
Date: Wed, 12 Sep 2007 17:25:07 -0500
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Date: 2007-09-12T17:25:07-05:00
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"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message
news:1189601170.835400.72630@w3g2000hsg.googlegroups.com...
> On 12 Wrz, 14:29, Stephen Leake <stephen_le...@stephe-leake.org>
> wrote:
>
> > The rule should be:
> >
> >     Constructors should not propagate exceptions up; they must handle
> >     all exceptions internally.
>
> No.
> What should the constructor do *after* handling the exception?
> Leave the object half-baked?

No, unbaked.

> Do you want to introduce additional states to the object design just
> to handle the "oops I'm not initialized" case?

No, because you must have those states anyway. Ada allows an object to be
finalized multiple times (either by an explicit call to Finalize, or in some
obscure cases involving aborts), so you have to have an invalid (not between
initialization and finalization) state in any Ada controlled object.
(Blindly doubly finalizing an object is likely to be a serious bug, because
of calling Unchecked_Deallocation twice on the same object or similar
gaffes.) Any controlled type that doesn't have an "I'm not valid" state is
wrong, period.

Once you have such a state, having an uninitialized object is not a
disaster.

                               Randy.