Programming Ruby

The Pragmatic Programmer's Guide

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module Comparable
Relies on: <=>

Index:

Comparisons between?


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


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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)).

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