lazy-bm.rb

require 'benchmark'
require "benchmark/memory"

N = 10_000_000

nonlazy   = ->{ (1..N)     .select(&:even?).map{|i| i*2 }.map{|i| i + 1 }.map(&:to_s).map(&:reverse).to_a.join(",").length }
lazy      = ->{ (1..N).lazy.select(&:even?).map{|i| i*2 }.map{|i| i + 1 }.map(&:to_s).map(&:reverse).to_a.join(",").length }
one       = ->{
  (1..N).each_with_object([]) do |i,a|
    if i.even?
      a << ((i*2)+1).to_s.reverse
    end
  end.join(",").length
}

nonlazy.() == lazy.() or fail
lazy.() == one.() or fail

puts "== CPU =="

Benchmark.bmbm do |x|
  x.report("nonlazy x#{N}", &nonlazy)
  x.report("lazy x#{N}", &lazy)
  x.report("one x#{N}", &one)
end

puts "== Memory =="

Benchmark.memory do |x|
  x.report("nonlazy x#{N}", &nonlazy)
  x.report("lazy x#{N}", &lazy)
  x.report("one x#{N}", &one)

  x.compare!
end

=begin

== CPU ==
Rehearsal -----------------------------------------------------
nonlazy x10000000   3.900000   0.310000   4.210000 (  4.235131)
lazy x10000000      9.330000   0.870000  10.200000 ( 10.258059)
------------------------------------------- total: 14.410000sec

                        user     system      total        real
nonlazy x10000000   3.700000   2.640000   6.340000 (  6.347430)
lazy x10000000      9.000000   1.220000  10.220000 ( 10.284903)
== Memory ==
Calculating -------------------------------------
   nonlazy x10000000   618.909M memsize (     0.000  retained)
                        10.000M objects (     0.000  retained)
                        50.000  strings (     0.000  retained)
      lazy x10000000     1.459B memsize (     0.000  retained)
                        35.000M objects (     0.000  retained)
                        50.000  strings (     0.000  retained)

Comparison:
   nonlazy x10000000:  618909008 allocated
      lazy x10000000: 1458914488 allocated - 2.36x more

(I implemented the 'one' option later, this is how it turned out:)

== CPU ==
Rehearsal -------------------------------------------------
one x10000000   3.090000   0.160000   3.250000 (  3.281496)
---------------------------------------- total: 3.250000sec

                    user     system      total        real
one x10000000   2.570000   0.040000   2.610000 (  2.628678)
== Memory ==
Calculating -------------------------------------
       one x10000000   458.909M memsize (     0.000  retained)
                        10.000M objects (     0.000  retained)
                        50.000  strings (     0.000  retained)