inject vs reduce

gistfile1.rb

require 'benchmark'

class Foo
  def initialize
    @bar = rand(100) # for caching
  end
  def bar
    @bar ||= rand(100)
  end
end

ARRAY = [].tap { |array| 1000.times { array << Foo.new } }
  
N = 5000

Benchmark.bmbm do |x|

  x.report('reduce') { N.times {
    ARRAY.map(&:bar).reduce(:+)
  } }

  x.report('inject') { N.times {
    ARRAY.inject(0){ |sum, entry| sum += entry.bar }
  } }
end

# Rehearsal ------------------------------------------
# reduce   4.010000   0.020000   4.030000 (  4.142364)
# inject   3.590000   0.000000   3.590000 (  3.828996)
# --------------------------------- total: 7.620000sec
# 
#              user     system      total        real
# reduce   3.900000   0.010000   3.910000 (  3.981650)
# inject   3.600000   0.010000   3.610000 (  3.676255)