On 8/29/2014 2:52 PM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schue...@gmx.net>"
wrote:
On Friday, 29 August 2014 at 19:01:51 UTC, Andrei Alexandrescu wrote:
On 8/29/14, 3:53 AM, "Marc Schütz" <schue...@gmx.net>" wrote:
Jacob Carlborg just recently brought this up in another thread. Isn't it
kind of consensus that calling a destructor from the GC is not a good
idea because of the restrictions that apply in this context? Andrei even
wanted to deprecate destructors for classes because of this. Maybe a
better direction would be to separate the concepts of destruction and
finalization, and introduce two kinds of "destructors" for them.
I think we need to stay with what we have. Adding a distinct kind of
destructor might be interesting. -- Andrei
Our idea was that an additional destructor (let's call it a finalizer)
would be helpful because it is backward compatible. The compiler could
make some validity checks on it, at the least make it nothrow, maybe
@nogc (but I believe we can relax this restriction), pure (?).
Disallowing access to references (because they could pointer to already
destroyed objects) is unfortunately not feasible, because we can't
distinguish GC pointers from other ones. To avoid the need for code
duplication, finalizers could always be called implicitly by destructors
(assuming everything that is allowed in finalizers is also permitted in
destructors).
Calling destructors from the GC could later be phased out. It is
technically not a breaking change, because there never was a guarantee
that they'd be called anyway.
I would say that all of those restrictions, except for nothrow, are
dependent on the current GC implementation. It is possible to write the
GC in such a way that you can do GC allocations in a destructor, as well
as access any GC references you want. The only thing with the GC
references is that there's no way to guarantee that the referenced
objects won't have already had their destructor called when the current
destructor is being called.
