Test ruby hash merging speed (#merge vs #merge!). Linked from: http://stackoverflow.com/questions/1972284/is-there-an-idiomatic-way-to-specify-default-values-for-optional-parameters-in-r#comment2298222_1972296

test_merges.rb

#!/usr/bin/env ruby

# To test is using `defaults.merge(options)` or `defaults.merge!(options)`
# is faster, I ran the following (manually replacing 'merge' with  'merge!'
# as appropriate):

10000000.times do
  defaults = {:a => 1, :b => 2, :c => 3, :d => 4}
  options = {:a => "another value", :d => true}
  options = defaults.merge!(options)
end

puts "done"

# And the run-times (in seconds, as reported by TextMate's
# script runner) were:
# 
# merge:  56.69, 57.15, 57.26     avg: 57.03 seconds
# merge!: 36.04, 36.18, 36.04     avg: 36.09 seconds