Moonbase

Noticed on ruby-talk:

When you create a Hash object in Ruby, you have the option of providing a block; when a hash lookup fails, this block will be called and its result returned instead of nil. The block is passed two parameters: the hash itself, and the requested key.

For example:

h = Hash.new { |h, k|
  "You asked for #{k}.  #{k} is not here."
}

puts h["Zordo"] # => You asked for Zordo.  Zordo is not here.

# See!  The hash is not modified by the callback, though
p h # => {}

# But it can be...
h2 = Hash.new { |h, k|
  puts "I sing of spleen."
  h[k] = "Respond, o ye #{k}!"
  "Hear me!"
}

puts h2["kumquats"] # => I sing of spleen.
                         Hear me!


# This time the lookup succeeds:
puts h2["kumquats"] # => Respond, o ye kumquats!