From: Robert Klemme <shortcutter@...>
Date: 2008-12-03T00:33:17+09:00
Subject: Re: Adventures in Optimization... or why CONST frozen is Good

2008/12/2 Brian Candler <b.candler@pobox.com>:
>> Now I have a class CONSTANT...
>>    UNDEFINED = 'U'.freeze
>>
>> and
>>    symbols_needed[symbol_name] = UNDEFINED
>
> Yes, that's the "right" solution with Ruby today, and you'll see this
> done in a lot of Ruby libraries. (Perhaps it would be nice if there were
> some syntax to define an inline frozen string literal)
>
> I don't consider this any sort of "optimisation" though. It's
> fundamental to the nature of Ruby that there is only one kind of value,
> which is a reference to an object. An assignment always copies only the
> reference.

Completely agree, this comes as no surprise. Actually, this is an
obvious design decision, if you want to use the same value to denote a
particular state then just use one object.

Another, probably more subtle issue is this:

irb(main):001:0> s="foo"
=> "foo"
irb(main):002:0> h={s=>1}
=> {"foo"=>1}
irb(main):003:0> s.equal? h.keys.first
=> false
irb(main):004:0> [s.object_id, h.keys.first.object_id]
=> [1073539250, 1073539280]
irb(main):005:0> s.freeze
=> "foo"
irb(main):006:0> h={s=>1}
=> {"foo"=>1}
irb(main):007:0> s.equal? h.keys.first
=> true
irb(main):008:0> [s.object_id, h.keys.first.object_id]
=> [1073539250, 1073539250]

In other words, there is a hidden dup going on if the Hash key is a
String which is not frozen.

Kind regards

robert

-- 
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