From: Rob Pitt <rob@...>
Date: 2006-06-17T21:11:11+09:00
Subject: Why does this code traversing iv_tbl using dl/struct via evil.rb not work?

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Hi all,

I seem to have misunderstood some finer point of how the instance  
variable tables work. Since for something like this I expect code  
speaks louder than words, I have made a small test case using evil.rb  
(to keep the file size down) available from:

http://rubyforge.org/cgi-bin/viewvc.cgi/evil/lib/evil.rb? 
revision=1.44&root=evil

Unfortunately, due to some error I have made this test case does not  
find all the instance variable keys. I'm sure some wizard out there  
will easily spot my newbie mistake. Could someone please point out  
where I'm going wrong by making this tiny test case work?

Many thanks,

Rob.


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require 'evil'
require 'test/unit'

class A;end
  
class TestSHStructs < Test::Unit::TestCase
  include RubyInternal
  
  def test_iv_tbl_traverse
    a = A.new
    located_keys = []
    created_keys = ['@foo', '@bar', '@baz', '@dave', '@jess', '@sally']
    created_keys.each do |key|
      a.instance_variable_set(key,1)
    end
    r_object = RObject.new(a.internal_ptr)
    table = ST_TABLE.new(r_object.iv_tbl)
    chain = 0
    while chain < table.num_bins
      table_entry = ST_TABLE_ENTRY.new(table.bins + (chain * DL::sizeof('P')))
      while table_entry
        sym = table_entry.key.to_sym 
        located_keys << sym.to_s if sym && sym.to_s[0] == ?@
        table_entry = table_entry.next && ST_TABLE_ENTRY.new(table_entry.next)
      end
      chain += 1
    end
    assert_equal(created_keys.sort,located_keys.sort)
  end
end
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