From: Robert Klemme <shortcutter@...>
Date: 2008-12-11T17:10:40+09:00
Subject: Re: why Hash corrupts 'key' object ?

2008/12/11 Dmitry Perfilyev <dmitry1976@gmail.com>:
> Hi, I have next script:
> t.rb:
> ===========================
> class TestStr < String
>  attr_accessor :dupstr
>  def initialize ( str )
>    @dupstr = str
>    super(str)
>  end
> end
> ts=TestStr.new("aaa")
> puts ts.dupstr
> h=Hash.new()
> h[ts]=true
> puts h.keys.first.class
> puts h.keys.first
> puts h.keys.first.dupstr
> ===========================
>
> run it:
>
> $ ruby t.rb
> aaa
> TestStr
> aaa
> nil
> $
>
> The question is - why there is 'nil' in the last line instead of "aaa" ?

Because Hash copies #dup an unfrozen String.

http://www.ruby-doc.org/core/classes/Hash.html#M002878

Try this:

class TestStr < String
 attr_accessor :dupstr
 def initialize ( str )
   @dupstr = str
   super(str)
 end
end
ts=TestStr.new("aaa")
puts ts.dupstr, ts.object_id
h=Hash.new()
h[ts]=true
puts h.keys.first.class, h.keys.first, h.keys.first.object_id,
h.keys.first.dupstr
puts "----"
ts.freeze
puts ts.dupstr, ts.object_id
h=Hash.new()
h[ts]=true
puts h.keys.first.class, h.keys.first, h.keys.first.object_id,
h.keys.first.dupstr

It is generally a bad idea to inherit core classes.  Delegation is
much better (see Mike's reply).

Cheers

robert


-- 
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