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require 'benchmark/ips'

Benchmark.ips do |b|

  hash = {}
  strings = Array.new(1000){('a'..'z').to_a.shuffle[0,15].join}
  symbols = strings.map &:to_sym
  index = nil
  require 'active_support/core_ext/hash/indifferent_access'

  b.report("strings to_sym in and out") do
    index = strings.sample
    hash[index.to_sym] = 'sample'
    hash[index.to_sym]
  end

  hash = {}

  b.report("symbols to_s in and out") do
    index = symbols.sample
    hash[index.to_s] = 'sample'
    hash[index.to_s]
  end
  hash = {}

  b.report("strings to_s in and out") do
    index = strings.sample
    hash[index.to_s] = 'sample'
    hash[index.to_s]
  end

  hash = {}.with_indifferent_access

  b.report("HWIA with string keys in and out") do
    index = strings.sample
    hash[index] = 'sample'
    hash[index]
  end

  hash = {}.with_indifferent_access

  b.report("HWIA with symbol keys in and out") do
    index = symbols.sample
    hash[index] = 'sample'
    hash[index]
  end

  hash = {}.with_indifferent_access

  b.report("HWIA with symbols to_s string keys in and out") do
    index = symbols.sample
    hash[index.to_s] = 'sample'
    hash[index.to_s]
  end

  b.compare!
end

Warming up --------------------------------------
strings to_sym in and out
                        30.830k i/100ms
symbols to_s in and out
                        43.916k i/100ms
strings to_s in and out
                        45.556k i/100ms
HWIA with string keys in and out
                        47.254k i/100ms
HWIA with symbol keys in and out
                        35.100k i/100ms
HWIA with symbols to_s string keys in and out
                        42.988k i/100ms
Calculating -------------------------------------
strings to_sym in and out
                        404.463k (± 4.2%) i/s -      2.035M
symbols to_s in and out
                        622.900k (± 3.9%) i/s -      3.118M
strings to_s in and out
                        690.458k (± 5.0%) i/s -      3.462M
HWIA with string keys in and out
                        723.858k (± 4.7%) i/s -      3.639M
HWIA with symbol keys in and out
                        469.217k (± 4.0%) i/s -      2.352M
HWIA with symbols to_s string keys in and out
                        634.770k (± 4.1%) i/s -      3.181M

Comparison:
HWIA with string keys in and out:   723858.3 i/s
strings to_s in and out:   690457.5 i/s - same-ish: difference falls within error
HWIA with symbols to_s string keys in and out:   634769.8 i/s - 1.14x slower
symbols to_s in and out:   622900.4 i/s - 1.16x slower
HWIA with symbol keys in and out:   469216.5 i/s - 1.54x slower
strings to_sym in and out:   404462.7 i/s - 1.79x slower