Benchmark for different approaches to Exercism's ruby track resistor color duo exercise

resistor_color_duo.rb

class ResistorColorDuo
  attr_reader :color_bands

  COLORS = { 'black'  => 0,
             'brown'  => 1,
             'red'    => 2,
             'orange' => 3,
             'yellow' => 4,
             'green'  => 5,
             'blue'   => 6,
             'violet' => 7,
             'grey'   => 8,
             'white'  => 9 }.freeze
  private_constant :COLORS

  def initialize(color_bands)
    @color_bands = color_bands
  end

  def value_map
    color_bands.map { |i| COLORS[i.downcase] }
               .join
               .to_i
  end

  def value_map_without_downcase
    color_bands.map { |i| COLORS[i] }
               .join
               .to_i
  end

  def value_inject
    color_bands.inject(0) do |previous_band, band|
      (previous_band * 10) + COLORS[band.downcase]
    end
  end

  def value_hash_access
    10*COLORS[color_bands[0]] + COLORS[color_bands[1]]
  end
end

require "benchmark"

n = 1_000_000
rcd = ResistorColorDuo.new(["violet", "yellow"])
padding = 20
Benchmark.bm(padding) do |x|
  x.report("value_map:")         { n.times do; rcd.value_map; end }
  x.report("value_map:")         { n.times do; rcd.value_map_without_downcase; end }
  x.report("value_inject:")      { n.times do; rcd.value_inject; end }
  x.report("value_hash_access:") { n.times do; rcd.value_hash_access; end }
end

#                            user     system      total        real
# value_map:             1.554845   0.010573   1.565418 (  1.615006)
# value_map:             1.319509   0.004232   1.323741 (  1.332095)
# value_inject:          0.658793   0.002375   0.661168 (  0.664390)
# value_hash_access:     0.225108   0.002511   0.227619 (  0.231068)