From: Robert Klemme <shortcutter@...>
Date: 2009-03-01T19:46:27+09:00
Subject: Re: Newbie question > Hash workings

2009/3/1 AD60 <andredeen@gmail.com>:
> Thank you both for seeing the light at the end of the tunnel. I fully
> understand what I have to do to get it working but just to clarify;

Good!

> By doing "h[2] << 20" I modified the original empty array I set as a
> default value and inserted no hash key because it is not an assignment
> to h?

Yes.  Although "assignment to h" is a bit ambiguous.  I guess you
meant the correct thing but keep in mind that normally "assignment to
h" means "h = something" and not "h[key] = something".  The latter is
actually a method defined in class Hash.

> Replacing the "h = Hash.new([])" with "h = Hash.new { |h,k| h[k] =
> []}" and just doing "p h[2]" before any assigment to h[2] has the
> surprising/logical side effect of creating a new key "2", thank god
> with value "[]" so no problems there, but still... I am now thinking
> that stating "h = Hash.new([])" is problematic idiom under all
> circumstances. Am I correct?

No, because it works well in other cases - the most popular probably being

counters = Hash.new 0
...
counters[foo] += 1

Kind regards

robert


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