From: Harry Ohlsen <harryo@...>
Date: 2003-08-07T05:19:32+09:00
Subject: Re: What's New and Shiny in Ruby 1.8.0?

On Thu, 7 Aug 2003 03:26, Ian Macdonald wrote:

> How does one use this with one's own objects, though?
>
> I just cooked up an example Person class to play with and then tried to
> sort it as above:
>
> class Person
>    include Enumerable
>
>    attr_accessor :first_name, :last_name, :age
>
>    def initialize(f,l,a)
>      @first_name = f
>      @last_name = l
>      @age = a.to_i
>    end
>  end
>
> p [d, g, i, j, p, j2, j3].sort_by { |x| [x.last_name, x.first_name, x.age]
> }
>
> and I get:
>
> ./sort_by:23: undefined method `[]' for #<Person:0x4014e37c>
> (NoMethodError)

I would guess that there's something in the code you didn't show (ie, that 
defines d, g, i, j, p, j2 and j3) that's causing this error message.

Here's an example that works just fine ...
----------------------
class Person
   include Enumerable

   attr_accessor :first_name, :last_name, :age

   def initialize(l,f,a)
     @first_name = f
     @last_name = l
     @age = a.to_i
   end

   def to_s
    "{#{@last_name}, #{@first_name}, #{@age}}"
   end
 end

a = Person.new("Wall", "Larry", 40)
b = Person.new("Matsumoto", "Yukihiro", 20)
c = Person.new("Van Rossum", "Guido", 30)

puts [a, b, c].sort_by { |x| [x.last_name, x.first_name, x.age] }.join("\n")

#=>
{Matsumoto, Yukihiro, 20}
{Van Rossum, Guido, 30}
{Wall, Larry, 40}
----------------------------------------------------------

Please note that those fake ages aren't intended to be accurate :-).