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Re: Wormholes

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On 9/3/12 6:12 PM, Roedy Green wrote:
> I run into this sort of problem fairly often.
>
> I have a method x that calls method y through a long chain of
> intermediate calls.
>
> I decide to add a feature.  Method x has access to information to
> decide if the feature should be implemented.  Method y is where the
> implementation is.
>
> Somehow I must pass information down the long chain from x to y.  This
> means changing the signatures of all the intermediate methods, and
> adjusting code to the new way.  This can cause ripples incommensurate
> with the triviality of the change.
>
> I imagined some sort of wormhole to allow information in one place to
> simply be known somewhere else without the excess exposure of public
> variables or tediously arranging transport.  I read about Eiffel a
> long time ago. IIRC you could provide a list of precisely who could
> see any given information.
>
> I wondered if anyone had thoughts on ways of tackling such a problem.
>

If you arrange to pass-through a Parameter Object instead of a bunch of 
related parameters, this could solve your problem in many (not all) cases.

The primary benefit of a Parameter Object is that you can add new fields 
(if they have sensible defaults) without a rippling change to all 
existing users of the method which takes the Parameter Object.

There are other potential benefits as well. Your Parameter Object might 
have a nice "Builder" counterpart which makes it easier to specify 
optional parameters (using call-chaining for example).

A special case of the Parameter Object is often called the Context. 
Many types of frameworks pass around a Context object to all methods. 
The HttpServletRequest object is such an example (a.k.a The Request 
Context). This is a more generic form than Parameter Object, and I don't 
suggest it for most usages, as you can end up with name-collisions, type 
problems, and other problems that can't be diagnosed at compile time.

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Thread

Wormholes Roedy Green <see_website@mindprod.com.invalid> - 2012-09-03 18:12 -0700
  Re: Wormholes eric@invalid.com (EricF) - 2012-09-04 02:06 +0000
    Re: Wormholes Roedy Green <see_website@mindprod.com.invalid> - 2012-09-04 10:08 -0700
    Re: Wormholes Wanja Gayk <brixomatic@yahoo.com> - 2012-09-09 13:55 +0200
  Re: Wormholes Arne Vajhøj <arne@vajhoej.dk> - 2012-09-03 22:34 -0400
    Re: Wormholes Stuart <DerTopper@web.de> - 2012-09-04 12:15 +0200
  Re: Wormholes markspace <-@.> - 2012-09-03 21:00 -0700
    Re: Wormholes Robert Klemme <shortcutter@googlemail.com> - 2012-09-04 07:08 +0200
  Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-04 08:47 +0200
    Re: Wormholes Lew <noone@lewscanon.com> - 2012-09-04 03:10 -0700
      Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-04 16:09 +0200
        Re: Wormholes Gene Wirchenko <genew@ocis.net> - 2012-09-04 08:34 -0700
          Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-04 17:46 +0200
            Re: Wormholes Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-09-04 09:31 -0700
        Re: Wormholes Lew <lewbloch@gmail.com> - 2012-09-04 11:14 -0700
        Re: Wormholes Arne Vajhøj <arne@vajhoej.dk> - 2012-09-04 19:59 -0400
    Re: Wormholes Roedy Green <see_website@mindprod.com.invalid> - 2012-09-04 13:20 -0700
      Re: Wormholes Arne Vajhøj <arne@vajhoej.dk> - 2012-09-04 20:00 -0400
      Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-05 09:01 +0200
      Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-05 09:02 +0200
      Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-05 09:02 +0200
        Re: Wormholes Zermelo <zermelo@teletu.it.nospam.invalid> - 2012-09-05 09:03 +0200
      Re: Wormholes markspace <-@.> - 2012-09-05 17:34 -0700
  Re: Wormholes Steven Simpson <ss@domain.invalid> - 2012-09-04 14:18 +0100
    Re: Wormholes Robert Klemme <shortcutter@googlemail.com> - 2012-09-05 21:51 +0200
      Re: Wormholes Steven Simpson <ss@domain.invalid> - 2012-09-05 23:26 +0100
        Re: Wormholes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-09-06 09:32 +0000
          Re: Wormholes Steven Simpson <ss@domain.invalid> - 2012-09-06 11:47 +0100
            Re: Wormholes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-09-06 15:10 +0000
              Re: Wormholes Steven Simpson <ss@domain.invalid> - 2012-09-06 20:12 +0100
                Re: Wormholes Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-09-06 21:08 +0000
  Re: Wormholes Nigel Wade <nmw@ion.le.ac.uk> - 2012-09-04 17:26 +0100
  Re: Wormholes Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-09-04 09:28 -0700
  Re: Wormholes David Lamb <dalamb@cs.queensu.ca> - 2012-09-04 16:54 -0400

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