bench.rb

require 'benchmark/ips'
require 'memoit'

class Tested
  def manual
    @manual ||= 123
  end

  def manual_hash(key)
    @manual_hash ||= {}
    @manual_hash[key] ||= 123 + key
  end

  memoize def memoit
    123
  end

  memoize def memoit_hash(key)
    key + 123
  end
end

tested = Tested.new

Benchmark.ips do |x|
  x.config(:time => 5, :warmup => 2)

  x.report("manual") do
    tested.manual
  end

  x.report("memoit") do
    tested.memoit
  end

  x.compare!
end

Benchmark.ips do |x|
  x.config(:time => 5, :warmup => 2)

  x.report("manual_hash_fixed") do
    tested.manual_hash(55)
  end

  x.report("memoit_hash_fixed") do
    tested.memoit_hash(55)
  end

  x.compare!
end

Benchmark.ips do |x|
  x.config(:time => 5, :warmup => 2)

  x.report("manual_hash_random") do
    tested.manual_hash(rand(100_000_000_000))
  end

  x.report("memoit_hash_random") do
    tested.memoit_hash(rand(100_000_000_000))
  end

  x.compare!
end

res.txt

Calculating -------------------------------------
              manual   121.076k i/100ms
              memoit    82.766k i/100ms
-------------------------------------------------
              manual      6.629M (± 1.3%) i/s -     33.175M
              memoit      2.487M (± 0.8%) i/s -     12.498M

Comparison:
              manual:  6628909.4 i/s
              memoit:  2486543.8 i/s - 2.67x slower

Calculating -------------------------------------
   manual_hash_fixed   108.751k i/100ms
   memoit_hash_fixed    58.607k i/100ms
-------------------------------------------------
   manual_hash_fixed      5.103M (± 1.3%) i/s -     25.556M
   memoit_hash_fixed      1.390M (± 1.2%) i/s -      6.974M

Comparison:
   manual_hash_fixed:  5103490.5 i/s
   memoit_hash_fixed:  1390457.4 i/s - 3.67x slower

Calculating -------------------------------------
  manual_hash_random    53.694k i/100ms
  memoit_hash_random    32.026k i/100ms
-------------------------------------------------
  manual_hash_random      1.080M (±14.1%) i/s -      5.208M
  memoit_hash_random    529.031k (±12.7%) i/s -      2.594M

Comparison:
  manual_hash_random:  1080078.4 i/s
  memoit_hash_random:   529031.2 i/s - 2.04x slower