Stringify hash keys

results.txt

% ruby -v
ruby 1.8.6 (2010-09-02 patchlevel 420) [i686-darwin13.1.0]
% ruby ./stringify_keys.rb
Rehearsal ------------------------------------------------
slow random:   1.750000   0.000000   1.750000 (  1.763713)
slow worst:    2.730000   0.040000   2.770000 (  2.768919)
fast random:   1.350000   0.000000   1.350000 (  1.355698)
fast worst:    2.520000   0.010000   2.530000 (  2.525618)
--------------------------------------- total: 8.400000sec

                   user     system      total        real
slow random:   1.740000   0.020000   1.760000 (  1.764548)
slow worst:    2.690000   0.030000   2.720000 (  2.726322)
fast random:   1.320000   0.000000   1.320000 (  1.318631)
fast worst:    2.390000   0.010000   2.400000 (  2.400333)
/tmp/foo %

% jruby -v
jruby 1.3.1 (ruby 1.8.6p287) (2009-06-15 2fd6c3d) (Java HotSpot(TM) 64-Bit Server VM 1.8.0) [x86_64-java]
% jruby ./stringify_keys.rb
Rehearsal ------------------------------------------------
slow random:   0.835000   0.000000   0.835000 (  0.682000)
slow worst:    0.440000   0.000000   0.440000 (  0.440000)
fast random:   0.927000   0.000000   0.927000 (  0.927000)
fast worst:    2.836000   0.000000   2.836000 (  2.836000)
--------------------------------------- total: 5.038000sec

                   user     system      total        real
slow random:   0.377000   0.000000   0.377000 (  0.377000)
slow worst:    0.464000   0.000000   0.464000 (  0.464000)
fast random:   0.674000   0.000000   0.674000 (  0.674000)
fast worst:    1.332000   0.000000   1.332000 (  1.332000)

% ruby -v
ruby 1.8.7 (2013-06-27 patchlevel 374) [i686-darwin13.0.0]
% ruby ./stringify_keys.rb
Rehearsal ------------------------------------------------
slow random:   2.110000   0.000000   2.110000 (  2.117278)
slow worst:    2.620000   0.040000   2.660000 (  2.656150)
fast random:   1.480000   0.000000   1.480000 (  1.490607)
fast worst:    2.060000   0.010000   2.070000 (  2.069680)
--------------------------------------- total: 8.320000sec

                   user     system      total        real
slow random:   1.900000   0.020000   1.920000 (  1.921963)
slow worst:    2.500000   0.030000   2.530000 (  2.538800)
fast random:   1.450000   0.000000   1.450000 (  1.467388)
fast worst:    2.210000   0.010000   2.220000 (  2.221262)

% ruby -v
ruby 1.9.3p545 (2014-02-24 revision 45159) [x86_64-darwin13.1.0]
% ruby ./stringify_keys.rb
Rehearsal ------------------------------------------------
slow random:   1.700000   0.020000   1.720000 (  1.735894)
slow worst:    2.080000   0.020000   2.100000 (  2.097329)
fast random:   0.830000   0.010000   0.840000 (  0.834736)
fast worst:    1.260000   0.000000   1.260000 (  1.262355)
--------------------------------------- total: 5.920000sec

                   user     system      total        real
slow random:   1.710000   0.020000   1.730000 (  1.741885)
slow worst:    2.130000   0.030000   2.160000 (  2.164398)
fast random:   0.780000   0.000000   0.780000 (  0.786673)
fast worst:    1.510000   0.000000   1.510000 (  1.519155)

% ruby -v
jruby 1.7.12 (1.9.3p392) 2014-04-15 643e292 on Java HotSpot(TM) 64-Bit Server VM 1.8.0-b132 +indy [darwin-x86_64]
% ruby ./stringify_keys.rb
Rehearsal ------------------------------------------------
slow random:   2.370000   0.040000   2.410000 (  1.085000)
slow worst:    0.600000   0.020000   0.620000 (  0.537000)
fast random:   1.650000   0.020000   1.670000 (  0.680000)
fast worst:    0.570000   0.010000   0.580000 (  0.526000)
--------------------------------------- total: 5.280000sec

                   user     system      total        real
slow random:   0.380000   0.010000   0.390000 (  0.370000)
slow worst:    0.590000   0.010000   0.600000 (  0.514000)
fast random:   0.360000   0.000000   0.360000 (  0.363000)
fast worst:    0.470000   0.010000   0.480000 (  0.464000)

stringify_keys.rb

require 'benchmark'

# NOT thread-safe
def stringify(options)
  # 1.8.6 (eventually) says: each': hash modified during iteration (RuntimeError)
  # 1.8.7 says: `each': hash modified during iteration (RuntimeError)
  # 1.9 says: `merge!': can't add a new key into hash during iteration (RuntimeError)
  # jruby-1.7.3 says: RuntimeError: can't add a new key into hash during iteration
  #                       merge! at org/jruby/RubyHash.java:1661

  options.each { |key, val| options.merge!(key.to_s => val) }
  options
end

# fixing thread-safety issue (only)
def stringify_slow(options)
  opts = options.dup
  opts.each { |key, val| options.merge!(key.to_s => val) }
  options
end

def stringify_fast(options)
  non_string_pairs = options.reject{|key, val| key.is_a?(String)}
  stringified_values = non_string_pairs.map{|key, val| [key.to_s, val]}

  if RUBY_VERSION < "1.8.7"
    stringified_values.flatten!
    options.merge!(Hash[*stringified_values])
  else
    options.merge!(Hash[stringified_values])
  end

  options
end

random_hash = {}
worst_case = {}

500.times do |i|
  key = i.to_s

  random_hash[rand() > 0.5 ? key.to_sym : key] = i
  worst_case[key.to_sym] = i
end

n = 1_000
Benchmark.bmbm(7) do |x|
  x.report("slow random:")   { for i in 1..n; stringify_slow(random_hash); end }
  x.report("slow worst:")    { for i in 1..n; stringify_slow(worst_case); end }
  x.report("fast random:")   { for i in 1..n; stringify_fast(random_hash); end }
  x.report("fast worst:")    { for i in 1..n; stringify_fast(worst_case); end }
end

The second implementation is thread-safe and looks (slightly) faster on every implementation but JRuby 1.3.1 (I put the blame on the flatten! plus splat - added only for the sake of compatibility).