brew/Library/Homebrew/os/mac/version.rb

require 'version'

module OS
  module Mac
    class Version < ::Version
      SYMBOLS = {
        :yosemite      => '10.10',
        :mavericks     => '10.9',
        :mountain_lion => '10.8',
        :lion          => '10.7',
        :snow_leopard  => '10.6',
        :leopard       => '10.5',
        :tiger         => '10.4',
      }

      def self.from_symbol(sym)
        str = SYMBOLS.fetch(sym) do
          raise ArgumentError, "unknown version #{sym.inspect}"
        end
        new(str)
      end

      def initialize(*args)
        super
        @comparison_cache = {}
      end

      def <=>(other)
        @comparison_cache.fetch(other) do
          v = SYMBOLS.fetch(other) { other.to_s }
          @comparison_cache[other] = super(Version.new(v))
        end
      end

      def to_sym
        SYMBOLS.invert.fetch(@version) { :dunno }
      end

      def pretty_name
        to_sym.to_s.split('_').map(&:capitalize).join(' ')
      end
    end
  end
end