Silly benchmark to satisfy my burning curiousity.

LAZY.md

$ ruby bench/lazy.rb
                                                                                                           user     system      total        real
using Range#lazy                                                                                       0.330000   0.000000   0.330000 (  0.330689)
using Enumerator#yield                                                                                 0.170000   0.000000   0.170000 (  0.177117)
using Fiber#yield                                                                                      0.340000   0.120000   0.460000 (  0.458015)

lazy.rb

require 'benchmark'

module LazyLists
  SECONDS_IN_A_DAY = 86400
  def using_range_lazy(start, n)
    r0 = (start..Float::INFINITY)
    r0.lazy.map { |x| x + SECONDS_IN_A_DAY }.first(n)
  end

  def using_enum_yield(start, n)
    Enumerator.new do |e|
      x = start
      while n > 0
        e.yield (x + SECONDS_IN_A_DAY)
        x = x + 1
        n -= 1
      end
    end.map { |x| x }
  end

  def using_fibers(start, n)
    f = Fiber.new do
      x = start
      loop do
        Fiber.yield x
        x = x + SECONDS_IN_A_DAY
      end
    end

    n.times { f.resume }
  end
end

Benchmark.bm(100) do |x|
  include LazyLists
  TIMES = 1_000_000
  START = 1
  x.report('using Range#lazy') do
    using_range_lazy(START, TIMES)
  end

  x.report('using Enumerator#yield') do
    using_enum_yield(START, TIMES)
  end

  x.report('using Fiber#yield') do
    using_fibers(START, TIMES)
  end
end