Test ruby hash merging speed (#merge vs #merge!).

test_merges.rb

#!/usr/bin/env ruby

# To test is using `defaults.merge(options)` or `defaults.merge!(options)`
# is faster, I ran the following:

Benchmark.bm(7) do |x|
  x.report("#merge:") do
    10000000.times do
      defaults = {:a => 1, :b => 2, :c => 3, :d => 4}
      options = {:a => "another value", :d => true}
      options = defaults.merge(options)
    end
  end

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

# on Ruby 2.6.7
#               user     system      total        real
# #merge:  11.822541   0.020036  11.842577 ( 11.905024)
# #merge!:  9.000405   0.000020   9.000425 (  9.016654)