Challenge 2: Comparable in Practice — Solution

class Temperature
  include Comparable
  attr_reader :celsius

  def initialize(celsius)
    @celsius = celsius
  end

  def <=>(other)
    celsius <=> other.celsius
  end
end

freezing = Temperature.new(0)
room = Temperature.new(21)
boiling = Temperature.new(100)

puts freezing < room
puts boiling > room
puts room.between?(freezing, boiling)

=begin
Output:
true
true
true

Notes:
- <=> is the only comparison method actually written by hand — it compares
  two Temperature instances by delegating straight to their underlying
  celsius values' own <=>.
- include Comparable mixes in <, >, <=, >=, ==, between?, and clamp, all
  implemented internally in terms of whatever <=> returns.
- freezing < room, boiling > room, and room.between?(...) all work
  correctly despite none of those three methods being defined anywhere in
  the Temperature class itself — they're entirely supplied by Comparable.
=end