From: Robert Klemme <shortcutter@...>
Date: 2009-04-16T18:45:47+09:00
Subject: Re: Tokenizing a large file

2009/4/16 Ryan Davis <ryand-ruby@zenspider.com>:
>
> On Apr 16, 2009, at 02:27 , Robert Klemme wrote:
>
>> Converted to the block form:
>>
>> def my_tokenize file
>>  tokens = Hash.new {|h,k| h[k.freeze] = k}
>
> FYI:
>
> % irb
>>> h = {}
> => {}
>>> h["key"] = 42
> => 42
>>> h.keys.map { |k| k.frozen? }
> => [true]
>
> hashes dupe and freeze string keys to prevent them from being mutated while
> hash keys.

Only if they are not frozen yet.

irb(main):001:0> h = {}
=> {}
irb(main):002:0> s = "abc"
=> "abc"
irb(main):003:0> h[s] = s
=> "abc"
irb(main):004:0> s = "bar".freeze
=> "bar"
irb(main):005:0> h[s] = s
=> "bar"
irb(main):006:0> h
=> {"abc"=>"abc", "bar"=>"bar"}
irb(main):007:0> h.each {|kv| p kv.map {|x| x.object_id}}
[134954550, 134972840]
[134951170, 134951170]
=> {"abc"=>"abc", "bar"=>"bar"}

Do you now know why I did it the way I did?

Cheers

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/