From: umptious@...
Date: 2006-12-07T07:00:12+09:00
Subject: YAML problem with cyclic data structures

I'm having a problem with YAML in the first slightly-more-than-toy
application that I've writing with it. Oddly, when I searched on "ruby
yaml cyclic" - the first phrase I thought of to get help - I found that
someone had written a program almost exactly like mine a year ago and
had the same problem:

>>>>>>
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/150930

I have a program that is trying to use YAML to save out its data,
without much success.
In the program, several of the classes have cyclic dependancies.
To be more specific, the program deals with "rooms" and "connections"
between the rooms, with each room and connection being represented as a
class.
Each room has up to 8 possible connections and each connection
contains, in turn, a reference to each of the two rooms it connects.
When YAML saves out its data for extremely simple graphs (2 or 3 rooms
interconnected), YAML spits out everything fine, and handles the cyclic
connections using ids to represent the same objects.
Problem seems to be that this is not working appropiately as the graph
grows in complexity (even 16 or so rooms can create issues).  YAML just
hangs when saving out the file or, at least, it takes exponentially
much, much, much longer to save the scene (I'm taking minutes vs. less
than a second for the 3 rooms).

Is this how it should be?  It seems like a bug in the YAML library to
me.
<<<<<<<<<<<<<<<<

He (or she) never got an answer.

The only things that I can add are:

1. That my Rooms and Doors are "owned" by references from a Floor
object and have only WeakRefs to each other

2.  Adding a single extra Door can increase YAML's save time from
several seconds to longer than the 20 minutes I was willing to wait

3. YAML seems quite happy coping with rooms arranged in a tree
structure, but a very few cycle inducing connections - literally 1 to 3
- will drive it crazy.

4. I've looked at my data structures very hard to make sure that they
are kosher. Or possibly halal.

Comments? I can think of ways around this quite easily for my program,
but I'd like to know what YAMLs limitations are, or if I might be doing
something wrong.

Btw - it seems odd that the Ruby YAML Cookbook doesn't contain the word
"cyclic"..