From: "Guy N. Hurst" <gnhurst@...>
Date: 2001-04-01T08:36:09+09:00
Subject: [ruby-talk:13400] Re: Multidimensional arrays and hashes?

Lloyd Zusman wrote:
> 
> Is it possible in ruby to make use of constructs that correspond to
> the following Perl constructs? ...
> 
>   $array[1][2][3] = 'whatever';   # multidimensional array
> 
>   $hash{'a'}{'b'} = 'something';  # multidimensional hash
>

Since (unlike perl) variables are not typed, ruby has no way to 
auto-vivify the particular structure you have in mind.

I mean, var could refer to a string, array, or hash.
And var[2] could refer to an array or hash.
(Hashes take any object as a key)

So, no, you can't do it outright -- you have to initialize
the variable as being an array or hash etc. first.

array=[]
array[1]=[]
array[1][2]=[]
array[1][2][3]='whatever'

But maybe you wish to avoid clearing out the
values if the arrays already partially exist?
Use ||= to protect them. This way, a new array
will only be assigned if it is currently nil; 
otherwise it will use the existing value.

array||=[]
array[1]||=[]
array[1][2]||=[]
array[1][2][3]='whatever'

Now, this is somewhat lengthy. Here's a shorter way:

(((array||=[])[1]||=[])[2]||=[])[3]='whatever'

Of course, this all could backfire if an existing value
is something other than an array...

Also, this is pretty ugly, to be sure, but matz has said that
he thinks it is a good practice to initialize first, anyway.

However, he is also open to a new construct as follows:

Hash.new{[]}    cf. [ruby-talk:04256]

In which case you'd be able to say

hash=Hash.new{ {} }	# default to a hash in this case
hash['a']['b']='something'

instead of:
((hash||={})['a']||={})['b']='something'


However, I don't recall seeing the same thing being
proposed for Array


Guy N. Hurst

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