From: Geoff Barnes <geofflbarnes@...>
Date: 2006-08-27T12:14:53+09:00
Subject: Nuby with instance_eval question

Wondering why this works the way it does:

      1 class Klass
      2
      3  attr_accessor :attr1
      4
      5  def initialize (&block)
      6          chum = "chum_in_Klass"
      7          instance_eval(&block) # Why does instance_eval pick up 
self.attr1 from Klass but not 'chum'??
      8          eval_attr1
      9  end
     10  def eval_attr1
     11          @ok = self.attr1.call
     12  end
     13 end
     14
     15 chum = "chum_in_main"
     16
     17 foo=Klass.new {
     18         self.attr1 = proc { chum }
     19 }
     20
     21 puts foo.inspect # -> foo.ok = "chum_in_main"
     22
     23 chum="chum_in_main_again"
     24 foo.eval_attr1
     25
     26 puts foo.inspect # -> foo.ok = "chum_in_main_again"

I have a constructor that uses a block to intialize the object's 
members.  Nested on the RHS of a member assignment is a proc block.  The 
proc block carries the value of chum from the "main" namespace, whereas 
I expected it would take the chum from the Klass.  I figured the proc 
would not be evaluated and bound to a namespace until the passed block 
was instance_eval'd in the constructpr, and thereby pick up a binding 
from Klass... This makes my head hurt!

The observed behaviour is what I want but I didn't think it was 
possible.  I want to make sure I'm not taking advantage of a "bug" or a 
language ambgiuity.  If someone could make my eval/proc light bulb come 
on it would be much appreciated..

Thanks

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