From: John Carter <john.carter@...>
Date: 2005-05-27T07:37:29+09:00
Subject: Re: hash of hash and complex data structure

On Fri, 27 May 2005, ngoc wrote:

> I am perl programmer, looking for new tools and interested in Ruby
> How in ruby similar to perl
> $a{$b}{$c}{$d} = 1;

Ruby doesn't quite have the auto-vivification that perl has. You have to 
be a little more explicit about specifying what the behaviour of the 
hash on accessing a uninited key should be eg..
Perl $a{fred}++
Will assume "quotes" around the fred, and the autovivify the $a{"fred"} as 
0 as you are adding one to it. Ruby doesn't quite do either.

You get something similar in Ruby by..
a = Hash.new(0)
a["fred"]+=1

You can get fancier in Ruby with...
a = Hash.new {|hash,key| hash[key] = Hash.new{
                  |hash,key| hash[key] = Hash.new(0)
              }}
a["tom"]["dick"]["harry"] += 1

On the other hand autovivifivation is a _very_ suprising feature of perl 
that took me years to find out about. I prefer ruby's more explicit 
approach.




John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
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