From: "Iñaki Baz Castillo" <ibc@...>
Date: 2011-04-15T21:50:42+09:00
Subject: Get the real object in a Hash key

Hi, let's suppose this simple code in which I add internal attributes
to String instances and use such String objects as Hash keys:

------------------------------------------------
h = {}

k1 = "aaa"
k1.instance_variable_set :@name, "Aaa-011"

k2 = "bbb"
k2.instance_variable_set :@name, "Bbb-268"

h[k1] = "Hello"
h[k2] = "Bye"
------------------------------------------------

Now I want to lookup in the hash the element whose key matches "aaa"
(using String#eql?):

  h["aaa"]
  => "Hello"

But I don't want just to get the key associated value ("Hello"), but
also the key object itself (not the "aaa" I passed but k1 object) so I
can check its @name attribute. And I need it in a very efficient way.

However I've realized right now that it's not possible. The hash key
doesn't store the given key as a reference to such object:

-------------------------------------------
puts k1.object_id
=> 18140060

puts k2.object_id
=> 16245980

h.keys.each {|k| puts k.object_id}
=> 16182220
=> 20359940
------------------------------------------.


I've realized of it while writting this mail, so forget the previous
question. Now I have another question:

--------------------
myobject = MyCustomClass.new

@h = {}

@h[myobject] = "lalalala"
--------------------

In this case, will Ruby GC delete myobject? or will it remain alive as
it has been used as a key of a hash (which is not GC'd in a supposed
code)?


Thanks a lot.
-- 
Iñaki Baz Castillo
<ibc@aliax.net>