Groups > comp.lang.java.programmer > #9744

Re: Immutable Datastructures with good Sharing

From	Daniel Pitts <newsgroup.nospam@virtualinfinity.net>
Newsgroups	comp.lang.java.programmer
Subject	Re: Immutable Datastructures with good Sharing
References	<j9292v$f69$1@news.albasani.net>
Message-ID	<UXTtq.21434$Pm3.19955@newsfe12.iad> (permalink)
Date	2011-11-07 08:46 -0800

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On 11/4/11 8:03 PM, Jan Burse wrote:
> Dear All,
>
> Value objects are some well known immutable
> datastructures, when an operation is applied,
> typically simply a new object is created. So
> for example doing:
>
> 3 = 1 + 2
>
> With java.lang.Integer objects would involve
> creating a new Integer with value left.intValue()
> + right.intValue().
>
> But instead of call the constructor, one can also call
> Integer.valueOf(), and there you have some sharing.
> Namely the class Integer caches the value objects for
> small values (at least the last time I looked into
> the Oracle source, it was there...).
>
> More elaborate sharing is seen in the String class
> by the substring() operation. This operation does
> reuse the original character array and only encapsulates
> the offset and the length in a new object. I wouldnt
> recomende that to get one character from a 1 MB
> long string, since it will prevent the original
> character array from GC. But in some situation this
> is quite handy.
>
> I am now looking for immutable datastructures with
> a similar sharing. In the String class example, the
> operation was substring() that produced a new immutable
> object. I am looking for:
>
> Some stack class, where: (Easy)
> pop() creates a new immutable stack
> push() creates a new immutable stack
> With good sharing.
>
> Some queue class, where: (Hard?)
> enqueue() creates a new immutable queue
> dequeue() creates a new immutable queue
> With good sharing.
>
> What is your favorite datastructure?
>
> Bye

Linked list will definitely work well as a "shared" stack object, 
because the "tail" of any given stack doesn't change with the operations.

As far as the queue goes, you run the risk of packratting if you share 
the underlying data structure. AFAIK, there are three common ways to 
implement a straight (as opposed to priority) queue.

   1. Linked lists with a head and tail reference
   2. Array list with a tail reference, and dequeue shifts all data.
   3. Array list with a head and tail reference. Known as a ring deque.

With the array approaches, you need to clear release the head reference 
on dequeue to avoid packratting. This happens automatically with the 
linked list. This means they can't be "immutable" as dequeue must be 
mutative.

For the linked list approach, enqueue is the problematic operation. A 
new tail must be appended and the old tail pointer made to point to it. 
  That operation changes the "next" value in the old tail.

So, you can decide "share on enqueue, copy on dequeue" or "copy on 
enqueue, share on dequeue". Based on requirements of your use-case, you 
can choose the appropriate alternative.  You can't have both, but if you 
can get halfway there.

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Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 04:03 +0100
  Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 12:42 +0100
    Re: Immutable Datastructures with good Sharing markspace <-@.> - 2011-11-05 09:35 -0700
      Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 19:33 +0100
        Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 14:42 -0400
          Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 19:52 +0100
            Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-05 19:32 +0000
            Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 15:31 -0400
              Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 20:50 +0100
                Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 16:26 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:35 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:38 +0100
                Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 16:59 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:06 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:41 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:42 +0100
                Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 17:11 -0400
            Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:20 -0400
              Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:33 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:38 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 21:41 +0100
                Re: Immutable Datastructures with good Sharing markspace <-@.> - 2011-11-05 17:20 -0700
                Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-05 22:13 -0300
                Re: Immutable Datastructures with good Sharing markspace <-@.> - 2011-11-05 20:05 -0700
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 10:27 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 10:14 +0100
    Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-05 10:06 -0700
      Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 10:55 -0700
        Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 19:30 +0100
          Re: Immutable Datastructures with good Sharing Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 18:16 -0400
            Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:20 +0100
            Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:38 +0100
        Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-05 17:47 -0300
        Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 14:26 -0700
      Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-05 16:14 -0400
  Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 14:35 -0700
    Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:42 +0100
      Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:50 +0100
      Re: Immutable Datastructures with good Sharing Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-11-05 14:51 -0700
        Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 22:58 +0100
          Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:03 +0100
            Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-05 23:07 +0100
            Re: Immutable Datastructures with good Sharing Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-11-06 09:44 +0200
              Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 10:22 +0100
                Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-06 09:05 -0400
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 14:16 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 14:22 +0100
                Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-06 14:30 +0000
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:02 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:08 +0100
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-06 16:18 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:54 +0100
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-06 17:31 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 22:33 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 16:47 -0500
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-06 16:58 +0100
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-07 01:01 +0000
                Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-06 17:26 -0800
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-07 23:45 +0000
                Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-06 14:44 -0800
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 17:51 -0500
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 01:28 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 19:50 -0500
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 02:13 +0100
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-06 20:20 -0500
                Re: Immutable Datastructures with good Sharing Lew <lewbloch@gmail.com> - 2011-11-06 17:29 -0800
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 11:22 +0100
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-06 23:02 +0000
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 00:32 +0100
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 01:10 +0100
                Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-07 10:24 +0000
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 11:52 +0100
                Re: Immutable Datastructures with good Sharing Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-07 11:12 +0000
                Re: Immutable Datastructures with good Sharing Arne Vajhøj <arne@vajhoej.dk> - 2011-11-07 17:24 -0500
                Re: Immutable Datastructures with good Sharing Giovanni Azua <bravegag@hotmail.com> - 2011-11-07 02:08 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 05:03 +0100
                Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 05:13 +0100
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-07 23:38 +0000
                Re: Immutable Datastructures with good Sharing Tom Anderson <twic@urchin.earth.li> - 2011-11-09 22:06 +0000
                Re: Immutable Datastructures with good Sharing Gene Wirchenko <genew@ocis.net> - 2011-11-09 18:02 -0800
  Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 00:28 +0100
    Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 00:39 +0100
      Re: Immutable Datastructures with good Sharing Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-11-06 20:57 -0400
        Re: Immutable Datastructures with good Sharing Jan Burse <janburse@fastmail.fm> - 2011-11-07 04:58 +0100
          Re: Immutable Datastructures with good Sharing Silvio Bierman <silvio@moc.com> - 2011-11-07 15:13 +0100
            Re: Immutable Datastructures with good Sharing Cthun <cthun_202@qmail.net.au> - 2011-11-07 12:54 -0500
              Re: Immutable Datastructures with good Sharing "B1ll Gat3s" <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-07 18:07 -0500
                Re: Immutable Datastructures with good Sharing B1ll Gat3s <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-07 22:07 -0500
                Re: Immutable Datastructures with good Sharing "B1ll Gat3s" <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-08 00:17 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-08 16:03 -0500
                Re: Immutable Datastructures with good Sharing Cthun <cthun_202@qmail.net.au> - 2011-11-08 15:49 -0500
                Re: Immutable Datastructures with good Sharing "B1ll Gat3s" <wm.g4t3s@m1cr0s0f7.c0m> - 2011-11-08 18:01 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-08 20:46 -0500
                Re: Immutable Datastructures with good Sharing "Cthun" <cthun_202@qmail.net.au> - 2011-11-08 22:43 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-09 08:28 -0500
                Re: Immutable Datastructures with good Sharing thoolen <th00len@th0lenbot.thorium> - 2011-11-08 16:00 -0500
  Re: Immutable Datastructures with good Sharing Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-11-07 08:46 -0800

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