Ruby's hash default value

default_value.rb

$x = 0
h = Hash.new {|h, k| h[k] = $x += 1 }
p h[:a]
p h[:a]
p h[:b]
p h

$y = 0
i = Hash.new { $y += 1 }
p i[:a]
p i[:b]
p i[:a]
p i

j = Hash.new(0)
p j[:a]
p j

broken = Hash.new { [] }
broken[:one] << 1
broken[:two] << 2
p broken  #=> {}

works = Hash.new {|h, k| h[k] = [] }
works[:one] << 1
works[:two] << 2
p works  #=> {:one=>[1], :two=>[2]}