From: Robert Klemme <shortcutter@...>
Date: 2011-08-03T16:13:38+09:00
Subject: Re: system stack error in ObjectSpace.each_object

On Wed, Aug 3, 2011 at 3:54 AM, luke gruber <luke.gru@gmail.com> wrote:
>>I would separate the leading from determining the set of instances to lead.

> I don't quite understand your example code.

There are two parts:

1. The method call propagation is done by instances of class Leader
which inherits BasicObject in order to have the minimum set of
predefined methods.  A Leader takes an Enumerable as source for
instances to delegate to, which means you can stuff in anything which
is Enumerable (e.g. Array, Set).

2. Then I created a class Source which is also Enumerable and happens
to look into ObjectSpace whenever someone wants to iterate via #each.
So, ObjectSpace would be only one way to look for instances.

>>class Module
>>  Source = Struct.new :cl do
>>    include Enumerable
>>
>>    def each(&b)
>>      return to_enum(:each) unless b
>>      ObjectSpace.each_object(cl, &b)
>
> ObjectSpace.each_object takes, as its first argument, a module.

... or a class.  Correct.

> I thought
> :cl was an instance variable of instances of the Source class. I don't
> know much about structs, so I'd love an explanation.

In the example "cl" is a member of the Struct which means there is a
pair of accessor methods, so "cl" really is a call to the getter.  And
the getter is set to "self" in Module#lemmings (which is an instance
method of all modules and classes).

Struct is really a handy way to quickly create a class with a few
properties which also gives you #hash and #eql?.  You can read more at
http://blog.rubybestpractices.com/posts/rklemme/017-Struct.html

Kind regards

robert

-- 
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