From: Gary Wright <gwtmp01@...>
Date: 2007-05-10T03:56:15+09:00
Subject: Re: using variables for the hash name and key name


On May 9, 2007, at 1:59 PM, Skye Weir-Mathews wrote:
> So, I'm trying to get the value out of the hash with
>
> @hash_name_var[@key_name_var]

The short answer is "don't do that".

If you need to select a particular hash dynamically, then
simply use another hash as an index:

master = { 'hash1' => { 'a' => 1 },
            'hash2' => { 'a' => 2, 'b' => 3}
}

puts master['hash1']['a']    # => 1
puts master['hash2']['b']    # => 3

Of course you can use an instance variable to
select a hash:

@hash_name = 'hash1'
puts master[@hash_name].inspect      # {'a' => 1}

There are other possibilities.  If you are only selecting between
a couple hashes:

	hash = case @select_hash
           when 'hash1' then @hash1
           when 'hash2' then @hash2
         end

         puts hash.inspect          # this will be @hash1 or @hash2

If for some reason these technique doesn't work you'll have
to start playing around with eval to get the indirection
you are looking for.

IMHO, the question you asked generally comes from Perl programmers
who are trying to emulate Perl's reference data type in Ruby.  That
is almost always the wrong approach in Ruby.

Gary Wright