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Re: Design thought for callbacks

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On Sat, Feb 21, 2015 at 1:44 PM, Cem Karan <cfkaran2@gmail.com> wrote:
> In order to inform users that certain bits of state have changed, I require them to register a callback with my code.  The problem is that when I store these callbacks, it naturally creates a strong reference to the objects, which means that if they are deleted without unregistering themselves first, my code will keep the callbacks alive.  Since this could lead to really weird and nasty situations, I would like to store all the callbacks in a WeakSet (https://docs.python.org/3/library/weakref.html#weakref.WeakSet).  That way, my code isn't the reason why the objects are kept alive, and if they are no longer alive, they are automatically removed from the WeakSet, preventing me from accidentally calling them when they are dead.  My question is simple; is this a good design?  If not, why not?  Are there any potential 'gotchas' I should be worried about?
>

No, it's not. I would advise using strong references - if the callback
is a closure, for instance, you need to hang onto it, because there
are unlikely to be any other references to it. If I register a
callback with you, I expect it to be called; I expect, in fact, that
that *will* keep my object alive.

ChrisA

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Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-21 16:42 +1100
  Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-21 18:03 +0200
    Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 07:10 -0500
      Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 14:12 +0200
        Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 08:42 -0500
          Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 15:54 +0200

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