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Re: Design thought for callbacks

From random832@fastmail.us
References (1 earlier) <CAPTjJmpEHQV2PpaZvszuTGn0_GNg0sWV6aLenbQsZrSXCy2YKQ@mail.gmail.com> <mailman.18957.1424524392.18130.python-list@python.org> <mcargl$h3k$1@reader1.panix.com> <mailman.19008.1424611304.18130.python-list@python.org> <cl2g0vFfiq9U1@mid.individual.net>
Subject Re: Design thought for callbacks
Date 2015-02-24 00:29 -0500
Newsgroups comp.lang.python
Message-ID <mailman.19117.1424755795.18130.python-list@python.org> (permalink)

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On Tue, Feb 24, 2015, at 00:20, Gregory Ewing wrote:
> Cem Karan wrote:
> > I tend to structure my code as a tree or DAG of objects.  The owner refers to
> > the owned object, but the owned object has no reference to its owner.  With
> > callbacks, you get cycles, where the owned owns the owner.
> 
> This is why I suggested registering a listener object
> plus a method name instead of a callback. It avoids that
> reference cycle, because there is no long-lived callback
> object keeping a reference to the listener.

How does that help? Everywhere you would have had a reference to the
"callback object", you now have a reference to the listener object.
You're just shuffling deck chairs around: if B shouldn't reference A
because A owns B, then removing C from the B->C->A reference chain does
nothing to fix this.

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Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-21 08:13 -0500
  Re: Design thought for callbacks Grant Edwards <invalid@invalid.invalid> - 2015-02-21 20:57 +0000
    Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-21 23:57 +0200
      Re: Design thought for callbacks Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-22 13:04 +1100
        Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-22 13:11 +1100
          Re: Design thought for callbacks Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-22 15:38 +1100
            Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-22 17:21 +1100
              Re: Design thought for callbacks Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-22 21:32 +1100
                Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-22 22:14 +1100
                Re: Design thought for callbacks Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-23 00:45 +1100
                Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-23 01:01 +1100
        Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 09:52 +0200
          Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-22 19:17 +1100
            Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 10:34 +0200
              Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-22 19:58 +1100
                Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 11:14 +0200
                Re: Design thought for callbacks Chris Angelico <rosuav@gmail.com> - 2015-02-22 21:21 +1100
                Re: Design thought for callbacks Laura Creighton <lac@openend.se> - 2015-02-22 12:28 +0100
                Re: Design thought for callbacks Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-23 00:57 +1100
                Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 16:06 +0200
    Re: Design thought for callbacks Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-22 00:05 -0700
    Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 08:21 -0500
      Re: Design thought for callbacks Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-24 18:20 +1300
        Re: Design thought for callbacks random832@fastmail.us - 2015-02-24 00:29 -0500
          Re: Design thought for callbacks Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-25 10:19 +1300
            Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-25 07:50 -0500
              Re: Design thought for callbacks Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-26 18:36 +1300
                Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-26 05:58 -0500
                Re: Design thought for callbacks Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-26 12:54 -0700
                Re: Design thought for callbacks Ethan Furman <ethan@stoneleaf.us> - 2015-02-26 12:00 -0800
                Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-03-02 06:06 -0500
                Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-03-02 06:04 -0500
                Re: Design thought for callbacks Ian Kelly <ian.g.kelly@gmail.com> - 2015-03-02 08:34 -0700
                Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-03-08 14:30 -0400

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