From: Rajinder Yadav <devguy.ca@...>
Date: 2009-10-14T10:40:45+09:00
Subject: Re: Enumerating and mixin.

Brian Candler wrote:
> Rajinder Yadav wrote:
>> OK I managed to sweet the code down to the following, is there anything 
>> else I
>> missed?
> 
> That's fine. So far your Vowels class doesn't really do anything more 
> than a simple Array would, but you've shown how your class gains methods 
> from the Enumerable module, and you can now add extra functionality 
> which is specific to a set of vowels. (This is composition by 
> delegation, an approach I highly recommend)
> 
> You mention <=>. This isn't needed here because each of the elements you 
> yield is a String, and strings already have <=> and so the elements can 
> be sorted. But if you want a different exercise, try:

Brian thanks for the demonstration of how to use Comparable, and also pointing 
out the other methods that can be redefined. If you didn't mention that, I would 
have stopped at <=>. Although I suspect the other methods make use of <=> 
internally?


> class Vowel
>   include Comparable
>   def initialize(v)
>     @v = v
>   end
>   def to_s
>     @v
>   end
>   def <=>(other)
>     @v <=> other.to_s
>   end
> end
> 
> v1 = Vowel.new("a")
> v2 = Vowel.new("e")
> v1 < v2    #=> true
> v3 = Vowel.new("e")
> v2 == v3   #=> true
> 
> Here you're exercising a different mixin, Comparable. It takes any class 
> which implements a <=> operator, and adds these methods for you:
> 
>>> Comparable.instance_methods
> => ["==", ">=", "<", "<=", ">", "between?"]
> 
> Regards,
> 
> Brian.


-- 
Kind Regards,
Rajinder Yadav

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