From: Ian Macdonald <ian@...>
Date: 2002-03-16T04:02:37+09:00
Subject: Re: new user confused by multidimensional Ruby hashes

On Fri 15 Mar 2002 at 19:18:06 +0900, you wrote:

> * 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 :)

Thank you very much. Your postings made things much clearer.

Ian
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