next_generation_of_measure.rb

# coding: utf-8
require 'measure'

DTP = Measure::Context.new do
  extend Measure::SIPrefixes

  unit :meter, "m"
  unit :inch, "in"
  unit :didot_point, "pt"

  alias_unit :cm, [:centi, :meter], "cm"
  alias_unit :mm, [:milli, :meter], "mm"
  alias_unit :m,  :meter
  alias_unit :pt, :didot_point

  scale q(1).in, q(254).quo(100).cm
  scale :inch, q(72).pt

  const :a4_paper => {
    :width  => q(210).mm,
    :height => q(297).mm,
  }
end

DTP.a4_paper[:width] #=> 210 [mm]
DTP[1].in #=> 1 [in]
DTP[2].in.to_cm #=> (127/25) [cm]
DTP[1].cm + DTP[5].mm #=> (15/10) [cm]
DTP[5].mm + DTP[1].m #=> 15 [mm]
DTP.eval { q(1).in + q(144).pt } #=> 3 [in]
DTP.eval { q(1) } #=> 1

JPY = Measure::Context.new do
  unit :円

  prefix :千, 1_000
  prefix :万, 10_000
  prefix :億, 100_000_000
  prefix :兆, 1_000_000_000_000

  alias_unit :千円, [:千, :円], "千円"
  alias_unit :万円, [:万, :円]
  alias_unit :億円, [:億, :円]
  alias_unit :兆円, [:兆, :円]
end

JPY[1].円 #=> 1 [円]
JPY[1].千円.to_円 #=> 1000 [円]
JPY[10].億円.to_千円 #=> 1000000 [千円]