Re: Creation and destruction responsibilities

From:

Andre Kostur <nntpspam@kostur.net>

Newsgroups:

comp.lang.c++

Date:

Tue, 4 Sep 2007 17:53:51 +0000 (UTC)

Message-ID:

<Xns99A16F53BD1A0nntpspamkosutrnet@209.135.99.21>

Miguel Guedes <miguel.a.guedes@gmail.com> wrote in
news:5NfDi.4344$5D.886@fe099.usenetserver.com:

I'd like some clarification on the correct way to destroy an object.

I've seen a couple of open source projects make use of object
factories to instantiate classes and smart pointers to destroy them
when the ref_count reaches zero. Something like:

pInstance = Factory::createSomething();

{
     smart_ptr<Something> ptr = pInstance
     .
    :
}

// out of scope: smart_ptr destroys pInstance

My question is, isn't a creator entity supposed to be responsible for
the destruction of the objects it creates? Isn't this one of the
golden rules of correct OO code design and what RAII is all about?

Would appreciate some clarification on this. Thank you.

Arguably, this code snippet _is_ the entity that created the object.
It's only that the creation is named "Factory::createSomething" and not
"new". However, I think that the smart_ptr should be made aware that
the appropriate disposal mechanism is called
"Factory::destroySomething" and not "delete". Otherwise smart_ptr would
be assuming normal new and delete.

Oh, and it would probably be better to:

{
  smart_ptr<Something> ptr(Factory::createSomething());
  .
  .
  .
}

No easy possibility of something using the naked pointer for anything
(unless you do "bad things" with ptr).

Then again, Factory::createSomething could even return a smart_ptr
<Something> instead of merely a Something*.