From: Thomas Wieczorek <wieczo.yo@...>
Date: 2008-08-24T21:27:35+09:00
Subject: Re: defining sort <=> for a class

Heya!

On Sun, Aug 24, 2008 at 2:03 PM, Adam Akhtar <adamtemporary@gmail.com> wrote:
> i tried this
>
> class Example
>
> attr_accessor :value
>
> def initialize
>    @value = 0
> end
>

Here's the error:

> def <=>(other_example)
>   @value <=> other_example
> end

You want to sort by the value, so you have to compare the values:

def <=>(other_example)
  @value <=> other_example.value
end

A simple example:
a = Example.new
b = Example.new
a.value = 10
arr = [a,b]
# => [#<Example:0x2b5d6a8 @value=10>, #<Example:0x2b5b7cc @value=0>]
arr.sort!
# => [#<Example:0x2b5b7cc @value=0>, #<Example:0x2b5d6a8 @value=10>],
means arr = [b, a]