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Re: when is destroy function called

by sundialsvc4 (Monsignor)
on Feb 27, 2013 at 18:29 UTC ( #1020941=note: print w/ replies, xml ) Need Help??


in reply to when is destroy function called

perldoc perlobj contains a definitive discussion both of destructors and of Perl’s garbage collector.   I think that the best way of thinking of both constructors and destructors is that they are “initialization” and “de-initialization” subroutines, respectively.   Of the two, destructors are less commonly used because they are less commonly required:   if there are no “unusual” storage-reference situations that might confuse the garbage collection algorithm, and no external resources to clean up, you often don’t need one.

As a rule of thumb, if you do something in the object’s constructor that is peculiar to that particular object instance and that has to be un-done, then you need to worry about defining a destructor.   But if you simply allocated a big data-structure that’s associated with the object, no worries, because the reference-count of all those things will also go to zero when the object itself does.   (Any exceptions to that rule will of course require an appropriate destructor.)

One thing that I can definitely say from very painful experience is this:   that you must never leave an ambiguous situation behind when your destructor completes.   If you “close” a socket, say, then immediately obliterate all memory of it (undef).   This is doubly true if you are indulging in fancy-pants designs involving subclasses of any sort.   Look carefully at the entire constructor and destructor sequences as your application grows.


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