From: JOSEPHJONES3247 <josephjones3247@...>
Date: 2011-04-22T09:20:48+09:00
Subject: Re: Using the spaceship operator

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Try it again. This time put uncapitalized "C" 



class MyTest < Array 





----- Original Message ----- 
From: "RichardOnRails" <RichardDummyMailbox58407@USComputerGurus.com> 
To: "ruby-talk ML" <ruby-talk@ruby-lang.org> 
Sent: Thursday, April 21, 2011 6:50:35 AM 
Subject: Re: Using the spaceship operator 

On Apr 21, 12:13 am, RichardOnRails 
<RichardDummyMailbox58...@USComputerGurus.com> wrote: 
> Hi, 
> 
> Here an abstract version of my app, in which I have an array of two- 
> element arrays I'd like to sort on the second element of each pair 
> using the spaceship operator: 
> 
> $data = [ [:A, 12], [:B, 30], [:C, 4] ] 
> 
> Class MyTest < Array 
> def <=>(other) 
> self[1] <=> other[1] 
> end 
> 
> @sorted_array = $date 
> end 
> 
> How can I make this work? 
> 
> Thanks in advance, 
> Richard 

Hi John and Brian, 

Thank you very much for your extremely insightful answers. 

I've been oscillating between: 
Metaprogramming Ruby 
The Well-Oriented Rubyist 
Design Patterns in Ruby 

But I didn't see anything in them for my sorting problem, so I Googled 
for it. Thus I found this concise method, but I couldn't figure out 
how to make "self" be my array of arrays. 

John: Thanks for that sort_by method using a block to return the 
specific value (from each element) I want the sort method to use. 
Very tidy! 

Brian: Thanks for 
1. addressing my key issue about how to make "self" be my array, so to 
speak. Question, would that redefinition of <=> contaminate uses of 
"sort" in other top-level classes? I could test for an answer, but I 
might miss something. 
2. using "delegation", which I've seen in those textbooks but not yet 
internalized. 

Best wishes, 
Richard 


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