Computing age in Ruby

benchmark.rb

# frozen_string_literal: true

require 'benchmark/ips'
require 'date'

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

  funcs = [
    ->(a, b) {
      (a.strftime('%Y%m%d').to_i - b.strftime('%Y%m%d').to_i) / 10000
    },

    ->(a, b) {
      (a.year - b.year) + (([a.month, a.day] <=> [b.month, b.day]) < 0 ? -1 : 0)
    },

    ->(a, b) {
      (a.year - b.year) + ((mdiff = a.month - b.month) < 0 || (mdiff == 0 && a.day < b.day) ? -1 : 0)
    },

    ->(a, b) {
      (((a.year * 100 + a.month) * 100 + a.day) - ((b.year * 100 + b.month) * 100 + b.day)) / 10000
    },
  ]


  today = Date.new(2020, 3, 16)
  cases = {
    Date.new(1990, 2, 10) => 30,
    Date.new(1990, 3, 16) => 30,
    Date.new(1990, 3, 17) => 29,
    Date.new(1990, 4, 10) => 29,
  }

  funcs.each_with_index { |func, i|
    cases.each { |date, expected_age|
      age = func[today, date]
      age == expected_age or abort "func[#{i}]: wrong result #{ages} instead of #{expected_age} when #{date} is given"
    }
  }

  funcs.each_with_index { |func, i|
    x.report("func[#{i}]") {
      cases.each_key { |date|
        func[today, date]
      }
    }
  }

  x.compare!
end

results.log

Warming up --------------------------------------
             func[0]    32.547k i/100ms
             func[1]    48.332k i/100ms
             func[2]   107.318k i/100ms
             func[3]    94.036k i/100ms
Calculating -------------------------------------
             func[0]    339.420k (± 5.9%) i/s -      1.692M in   5.005850s
             func[1]    567.619k (± 3.0%) i/s -      2.852M in   5.028401s
             func[2]      1.325M (± 3.7%) i/s -      6.654M in   5.029764s
             func[3]      1.147M (± 3.2%) i/s -      5.736M in   5.007488s

Comparison:
             func[2]:  1324806.2 i/s
             func[3]:  1146738.6 i/s - 1.16x  slower
             func[1]:   567619.0 i/s - 2.33x  slower
             func[0]:   339419.8 i/s - 3.90x  slower