# 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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