Challenge 3: Sorting Custom Objects — Solution

class Temperature
  include Comparable
  attr_reader :celsius

  def initialize(celsius)
    @celsius = celsius
  end

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

  def to_s
    "#{celsius}°C"
  end
end

readings = [
  Temperature.new(21),
  Temperature.new(-5),
  Temperature.new(100),
  Temperature.new(0),
  Temperature.new(37)
]

sorted = readings.sort
puts sorted.map(&:to_s).join(", ")

=begin
Output:
-5°C, 0°C, 21°C, 37°C, 100°C

Notes:
- readings.sort is called with no block and no explicit comparison logic
  passed in at all — Array#sort automatically uses each element's <=>
  method when nothing else is provided.
- Because Temperature defines <=> (and includes Comparable, which relies
  on it), .sort produces a correctly ordered array with zero extra code
  written specifically for sorting.
- .map(&:to_s) uses the Symbol#to_proc shorthand from Course 1 Chapter 8
  to convert each Temperature into its string form for a readable one-line
  printout, using the to_s override defined above.
=end