module Comparable

Relies on: <=>

The Comparable mixin is used by classes whose objects may be ordered. The class must define the <=> operator, which compares the receiver against another object, returning -1, 0, or +1 depending on whether the receiver is less than, equal to, or greater than the other object. Comparable uses <=> to implement the conventional comparison operators (<, <=, ==, >=, and >) and the method between?.

class SizeMatters
  include Comparable
  attr :str
  def <=>(anOther)
    str.size <=> anOther.str.size
  end
  def initialize(str)
    @str = str
  end
  def inspect
    @str
  end
end

s1 = SizeMatters.new("Z")
s2 = SizeMatters.new("YY")
s3 = SizeMatters.new("XXX")
s4 = SizeMatters.new("WWWW")
s5 = SizeMatters.new("VVVVV")

s1 < s2 → true
s4.between?(s1, s3) → false
s4.between?(s3, s5) → true
[ s3, s2, s5, s4, s1 ].sort → [Z, YY, XXX, WWWW, VVVVV]

instance methods

Comparisons: anObject < otherObject → true or false; anObject <= otherObject → true or false; anObject == otherObject → true or false; anObject >= otherObject → true or false; anObject > otherObject → true or false; Compares two objects based on the receiver's <=> method.
between?: anObject.between?( min, max ) → true or false; Returns false if anObject <=> min is less than zero or if anObject <=> max is greater than zero, true otherwise.
3.between?(1, 5) → true 6.between?(1, 5) → false 'cat'.between?('ant', 'dog') → true 'gnu'.between?('ant', 'dog') → false

Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"

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