From: Thomas Hurst <tom.hurst@...>
Date: 2002-03-15T19:18:06+09:00
Subject: Re: new user confused by multidimensional Ruby hashes

* Thomas Hurst (tom.hurst@clara.net) wrote:

> * Ian Macdonald (ian@google.com) wrote:

> > [ianmacd@caliban ~]$ irb
> > irb(main):001:0> foo = Hash.new( {} )
> > {}
>
> Note: what you've actually done here is:
>
> irb(main):001:0> foo = Hash.new(Hash.new)
> {}
>
> Which is really just a funny one dimensional hash (you didn't specify a
> key for the second hash, so everything references it, oops):

Er, <cue explanation *not* written at 3am with a rat trying to tear off
my back>

What you've actually done is specify a hash who's default value is
another hash object; that means unless you specify otherwise every hash
index references that same object.

To have Hash.new evaluated to create a new object each time, you need to
pass it a block, but that's only supported in 1.7 (although you should
be able to override Hash#[] to provide this functionality if you really
need it), otherwise you need to do it manually.

Hope that's a bit clearer :)

-- 
Thomas 'Freaky' Hurst  -  freaky@aagh.net  -  http://www.aagh.net/
-
Honesty pays, but it doesn't seem to pay enough to suit some people.
		-- F.M. Hubbard