Compare performance of ||= vs Hash.new for default arrays

oror_vs_hash_new.rb

require 'benchmark'

N = 10_000
C = %w[a b c] * 100

Benchmark.bmbm do |x|
  x.report "||=" do
    N.times do
      C.each_with_object({}) do |val, memo|
        memo[val] ||= []
        memo[val] << val
      end
    end
  end

  x.report "Hash.new" do
    N.times do
      hash = Hash.new { |h, k| h[k] = [] }

      C.each_with_object(hash) do |val, memo|
        memo[val] << val
      end
    end
  end
end

results.txt

Rehearsal --------------------------------------------
||=        0.860000   0.010000   0.870000 (  0.867042)
Hash.new   0.620000   0.000000   0.620000 (  0.623793)
----------------------------------- total: 1.490000sec

               user     system      total        real
||=        0.850000   0.010000   0.860000 (  0.856867)
Hash.new   0.600000   0.000000   0.600000 (  0.603829)