inject vs plus

inject_vs_plus.rb

require 'benchmark'

class PerfTest
  def with_inject(array)
    mapped_vals.inject(array, :<<)
  end

  def with_plus(array)
    array + mapped_vals
  end

  def with_each(array)
    mapped_vals.each {|i| array << i }
    array
  end

  private
  def mapped_vals
    (1..1_000_000).map do |i|
      i * i * i * i
    end
  end
end

Benchmark.bmbm do |bm|
  bm.report("with inject") { PerfTest.new.with_inject([1, 2, 3, 4, 5]) }
  bm.report("with plus") { PerfTest.new.with_plus([1, 2, 3, 4, 5]) }
  bm.report("with each") { PerfTest.new.with_each([1, 2, 3, 4, 5]) }
end

results

Ξ code/doodles → ruby inject_vs_plus.rb
Rehearsal -----------------------------------------------
with inject   1.330000   0.040000   1.370000 (  1.514304)
with plus     0.900000   0.010000   0.910000 (  0.906701)
with each     1.260000   0.030000   1.290000 (  1.529601)
-------------------------------------- total: 3.570000sec

                  user     system      total        real
with inject   1.080000   0.010000   1.090000 (  1.323706)
with plus     0.890000   0.010000   0.900000 (  0.899643)
with each     1.450000   0.030000   1.480000 (  1.961771)