Ruby DSL: define_unit

module TinyUnits

  def self.define_unit(name, quantity, *aliases)

    Numeric.module_eval do

      define_method(name) { self * quantity }

      aliases.each { |ali| alias_method ali, name }

    end

    define_method(name) { |x| x / quantity }

    aliases.each do |ali|

      alias_method ali, name

      module_function ali

    end

    module_function name

  end

  private_class_method :define_unit

  

  define_unit :cm, 0.01

  define_unit :mm, 0.1.cm

  define_unit :inch, 2.54.cm, :in

  define_unit :feet, 12.inch, :ft

  define_unit :yard, 3.feet

  define_unit :mile, 1760.yard

end

1.cm # => 0.01

2.mm # => 0.002

3.ft # => 0.9144

4.mile # => 6437.376

tall = 6.ft + 2.in # => 1.8796

include TinyUnits

cm(tall) # => 187.96