Re: Are throwing default constructors bad style, and if so, why?

From:
Andrei Alexandrescu <SeeWebsiteForEmail@erdani.org>
Newsgroups:
comp.lang.c++.moderated
Date:
Tue, 23 Sep 2008 19:07:11 CST
Message-ID:
<48D83D61.906@erdani.org>
Erik Wikstr??m wrote:

On 2008-09-21 23:44, Andrei Alexandrescu wrote:

Erik Wikstr??m wrote:

On 2008-09-20 08:23, Andrei Alexandrescu wrote:

The advantage of separating teardown from deallocation is that there are
no more dangling pointers, and consequently even incorrect programs
could achieve predictable, reproducible, and consequently debuggable
behavior. That way you get to use GC for what it's best at (recycling
memory) and deterministic teardown for what it's best at (timely release
of resources). In fact I'd go as far as saying that I think separating
teardown from deallocation an essential ingredient in successfully
marrying deterministic teardown with garbage collection. Other schemes
could be conceived, and I've thought of a few, but at least those I
could imagine lead to a m??salliance at most.

This really is not my area of expertise, but I fail to see how leaving
the object in an zombie-state will improve when it comes to dangling
pointers. After all, sooner or later the GC will come and collect the
used memory and it might be used by some other object. So at most you
manage to hide the fact that you are using an invalid pointer a bit longer.

The GC recycles memory when by definition the program cannot reach it.
This excludes a number of oddities such as forging pointers, but by and
large it can be used as an axiom.


I just assumed that the GC would be allowed to collect any object whose
destructor had run, kind of like mark and sweep. This way you don't have
to do the reachability scan as often since it would only be for litter-
collection, and you would also know that the destructors of those non-
reachable objects found had not been run.


I think that design would work too. But I don't like that it allows
dangling pointers.

Andrei

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