From: Alex Young <alex@...>
Date: 2007-07-04T18:13:43+09:00
Subject: Re: Isn't hash default value behavior just a little bizarre?

Farhad Farzaneh wrote:
> Pe単a, Botp wrote:
> 
>> ruby allows one to change the default value. that is good, imho.
>> i think the surprise stems fr the fact that it is _too simple to change 
>> the default. hey, it's ruby ;)
>>
>> kind regards -botp
> 
> You're right.  Somehow I missed that in the documentation.... did RTFM, 
> but obviously not carefully enough.
> 
> Still, I do find it pretty surprising.  I got stung when I was actually 
> using the feature to initialize any entry to an array just to avoid the 
> business of
> 
> hash[key] ||= []
> 
Apologies if you've already come across this, but I think the correct 
way to do what you're trying to do is this:

h = Hash.new(){|h,k| h[k] = []}

The block passed to Hash.new gets called for each new entry in the hash, 
  so a new array will be constructed each time.

Hope this helps,
-- 
Alex