From: Martin DeMello <martindemello@...>
Date: 2003-08-07T07:43:54+09:00
Subject: Re: What's New and Shiny in Ruby 1.8.0?

Harry Ohlsen <harryo@zip.com.au> wrote:
> but I can't think of a way to get it to work for strings, for example. Maybe 
> if strings had a unary minus that changed every character to the character 
> with code (255 - ascii-code) ... but that sounds like a real hack :-).  Of 
> course, it's not general enough, either.

Still hacky, but general:

class Test
  attr_accessor :foo, :bar
  def initialize(f, b)
    @foo, @bar = f, b
  end

  def inspect
    "[#{foo}, #{bar}]"
  end
end

def rev(obj)
  a = obj.dup
  class << a
    alias old_cmp <=>
    def <=>(other)
      -old_cmp(other)
    end
  end
  a
end

a = [
  Test.new("Hello", 1),
  Test.new("World", -1),
  Test.new("Foo", 5),
  Test.new("bar", 4)
]

p a
p a.sort_by {|x| x.foo}
p a.sort_by {|x| rev(x.foo)}

martin