From: Robert Klemme <shortcutter@...>
Date: 2011-04-15T22:48:21+09:00
Subject: Re: Get the real object in a Hash key

On Fri, Apr 15, 2011 at 3:14 PM, Iņaki Baz Castillo <ibc@aliax.net> wrote:
> 2011/4/15 Robert Klemme <shortcutter@googlemail.com>:
>> On Fri, Apr 15, 2011 at 2:50 PM, Iņaki Baz Castillo <ibc@aliax.net> wrote:
>>> 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:
>>
>> This is a special optimization for unfrozen Strings as Hash keys.
>
> Oopss, if I freeze the string before inserting it as Hash key it
> doesn't occur (I get some object_id) :)
> Same occurs if I use a class inheriting from String. Good to know!
>
>
> Then I come back to my original question:
>
> ----------------
> k1 = "aaa"
> k1.freeze
>
> h = {}
>
> h[k1] = "HELLO"
> ----------------
>
> Given a string "aaa", how can I get the object k1 from the hash? (I
> mean without comparing String#eql? each key with the string "aaa")
> Unfortunatelly I think Hash class does not provide a method for it.

Exactly.  And you don't want to do it.  A Hash is an associative
storage which associates the value with your key.  If you need to
stuff in more information - you need to add it to the value and not
the key.  The simplest would be to define a Struct, e.g.

Value = Struct.new :name, :val

Then put this into the Hash as values

h[k1] = Value["a name", "HELLO"]

Kind regards

robert

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