From: Brian Candler <B.Candler@...>
Date: 2007-05-10T05:57:55+09:00
Subject: Re: using variables for the hash name and key name

On Thu, May 10, 2007 at 03:56:15AM +0900, Gary Wright wrote:
> 
> 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.

Or if the values are in instance variables, you can use
instance_variable_get.

@a = "one"
@b = "two"
which = "@a"
puts instance_variable_get(which)