You can autovivify in Ruby with my XKeys Gem.

require 'xkeys'
z = [].extend XKeys::Auto
z[0, 8] = z[1, 11] = ... = z[1, 4] = 'o'
[download]

And

node_info = {}.extend XKeys::Auto
node_info['list', :[], 'name'] = 'new node' # :[] means next index
#  {"list"=>[{"name"=>"new node"}]}
[download]