Re: The current object

From	Andrew Haley <andrew29@littlepinkcloud.invalid>
Subject	Re: The current object
Newsgroups	comp.lang.forth
References	(20 earlier) <kmm6b0$9bd$1@online.de> <518f7fbb$0$32105$14726298@news.sunsite.dk> <kmrrtk$8nm$1@online.de> <_Lmdnbce8uElYQzMnZ2dnUVZ_sidnZ2d@supernews.com> <kmtp8h$iof$1@online.de>
Message-ID	<6IGdnc1P2b8tDg_MnZ2dnUVZ_ridnZ2d@supernews.com> (permalink)
Date	2013-05-14 14:42 -0500

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Bernd Paysan <bernd.paysan@gmx.de> wrote:
> Andrew Haley wrote:
> 
>> Bernd Paysan <bernd.paysan@gmx.de> wrote:
>>> Note that this doesn't really work.  For the user of an object, it's
>>> a black box (you can't access the ivars directly), but for derived
>>> classes, it's a "grey box" - you *can* access the ivars.
>> 
>> IMO this is wrong -- it breaks encapsulation.  A subclass shouldn't
>> access ivars any more than any other class.  (But, of course, I am not
>> saying that a mechanism should prevent it, just that there's nothing
>> special about subclasses.)
> 
> Really?  I think this is obsessive encapsulation, and probably
> originates in the "interface" concept: You define an interface,
> which is a set of selectors.  And then you have various classes
> implementing that interface - as the interface itself does not have
> ivars, the classes don't share any ivars.

Well, yes.  The point is that you can't possibly know what subclasses
people have written, so if you want the flexibility to change how your
class is implemented -- and you surely do -- then you can't give
subclasses interior access.

>> Sure, but it's harder than that because not only do people want a
>> particular behaviour, they also insist on how it works internally.
>> We'll never get anywhere unless people can relax that.
> 
> Yes.  But that follows a typical Forth tradition: that you don't
> encapsulate things.
> 
> However, this is not really impossible to solve in an OOP framework:
> The interface defines the behavior, and each class can implement it
> as it likes to.

But why?  All you really need is a fast and reasonably general
dispatch machanism, like the LISP virtual function.

> The MOP would define the interface, and the actual object system
> would define the implementation.

That sounds far from ideal to me.  Surely the Forth system itself can
do far better by using things like inline caches.

> So far, I've identified:
> 
> * People want different modes for sending messages - object on stack
> or not (Swoop actually already has these two modes, so this is not a
> new requirement).
> 
> * People want different modes for defining methods: current object,
> current object for ivars and object on stack for messages, or object
> on stack for both.  Or a "this" local variable instead of a current
> object...
> 
> * People are very performance sensitive, so they want to tune
> things.  Forth compilers are usually quite simple, so proposing
> invocation styles that require complex compilers (like trace
> schedulers) are not an option.

I'm pretty sure that if the Forth system itself provides fast dispatch
a la virtual functions it can do a better job.

> * We see "old and proven" arguments, which is the standard argument
> against any change.  Because it implies that "new" means "unproven".

Straw man.  Forget it.

Andrew.

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The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-01 17:01 +0000
  Re: The current object (was: Went open source with my GA144 ...) albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-01 19:20 +0000
    Re: The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-02 17:02 +0000
  Re: The current object (was: Went open source with my GA144 ...) Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-02 02:12 +0200
    Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-02 04:52 -0400
    Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-02 04:31 -0500
      Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-02 18:25 +0200
        Re: The current object anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-02 16:58 +0000
          Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-02 22:26 +0200
            Re: The current object anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-06 14:52 +0000
              Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 03:47 +0200
                Re: The current object anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-07 15:22 +0000
        Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-02 12:12 -0500
          Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-02 21:56 +0200
            Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-03 03:19 -0500
            Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-03 06:54 -0400
    Re: The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-02 14:28 +0000
      Re: The current object (was: Went open source with my GA144 ...) Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-02 19:58 +0200
        Re: The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-03 16:50 +0000
          Re: The current object (was: Went open source with my GA144 ...) Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-04 18:58 +0200
            Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-04 13:35 -0500
              Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-05 01:08 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-04 18:29 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-05 03:00 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-05 03:48 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-05 23:15 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-06 05:01 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 03:23 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-07 03:39 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 19:00 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-07 13:34 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 22:00 +0200
                Re: The current object anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-08 07:26 +0000
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-05 06:39 -0400
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-05 09:15 -0500
                Re: The current object Paul Rubin <no.email@nospam.invalid> - 2013-05-05 09:25 -0700
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-05 11:43 -0500
                Re: The current object Paul Rubin <no.email@nospam.invalid> - 2013-05-05 09:59 -0700
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-06 05:06 -0500
                Re: The current object Mark Wills <forthfreak@gmail.com> - 2013-05-06 00:19 -0700
                Re: The current object "WJ" <w_a_x_man@yahoo.com> - 2013-05-13 22:45 +0000
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-05 06:39 -0400
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-05 23:40 +0200
            Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-05 06:39 -0400
              Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-05 23:29 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-06 05:10 -0500
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-08 07:35 -0400
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-09 00:06 +0200
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-09 06:41 -0400
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-11 21:31 +0200
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-12 07:40 -0400
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-14 01:10 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-14 03:58 -0500
                Re: The current object anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-14 14:51 +0000
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-15 03:48 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-14 18:37 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-14 14:42 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-15 00:22 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-15 02:56 -0500
                Re: The current object stephenXXX@mpeforth.com (Stephen Pelc) - 2013-05-15 13:52 +0000
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-15 17:58 +0200
                Re: The current object albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-17 14:01 +0000
                Re: The current object johno <email@address.com> - 2013-05-15 22:38 +0100
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-14 06:27 -0400
                Re: The current object albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-09 16:06 +0000
            Re: The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-06 16:12 +0000
              Re: The current object (was: Went open source with my GA144 ...) Alex McDonald <blog@rivadpm.com> - 2013-05-06 10:25 -0700
              Re: The current object (was: Went open source with my GA144 ...) Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 04:00 +0200
                Re: The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-07 15:02 +0000
              Re: The current object (was: Went open source with my GA144 ...) Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 04:09 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-07 03:41 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 19:02 +0200
                Re: The current object (was: Went open source with my GA144 ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-07 14:33 +0000
                Re: The current object (was: Went open source with my GA144 ...) Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-07 19:40 +0200
        Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-15 16:46 +0200
          Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-15 13:11 -0500
            Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-15 23:23 +0200
              Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-16 02:24 -0500
                Re: The current object anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-16 13:55 +0000
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-16 17:45 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-18 05:13 -0500
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-18 06:43 -0400
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-18 10:03 -0500
                Re: The current object Doug Hoffman <glidedog@gmail.com> - 2013-05-18 11:30 -0400
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-19 01:20 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-19 12:33 -0500
                Re: The current object Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-19 01:07 +0200
                Re: The current object Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-19 03:58 -0500
            OO dispatch (was: The current object) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-16 14:07 +0000
              Re: OO dispatch Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-18 05:28 -0500
                Re: OO dispatch anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-20 11:28 +0000
                Re: OO dispatch Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-20 09:00 -0500
                Re: OO dispatch Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-21 01:37 +0200
                Re: OO dispatch Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-21 03:21 -0500
                Re: OO dispatch anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-21 12:24 +0000
                Re: OO dispatch Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-21 10:18 -0500
                Re: OO dispatch anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-21 16:03 +0000
                Re: OO dispatch Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-05-21 12:55 -0500
                Re: OO dispatch Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-29 00:00 +0200
                Re: OO dispatch Mark Wills <markrobertwills@yahoo.co.uk> - 2013-05-28 15:49 -0700

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