From: "Florian Groß" <florgro@...>
Date: 2005-11-09T23:59:36+09:00
Subject: Re: memoize and yaml

Brian Buckley wrote:

>>module Memoize
>>   def memoize(name)
>>     name = name.to_sym
>>     old_method = instance_method(name)
>>     remove_method(name)
>>
>>     define_method(name) do |*args|
>>       @cache ||= {}
>>       signature = [name] + args
>>
>>       if @cache.include?(signature) then
>>         @cache[signature]
>>       else
>>         @cache[signature] = old_method.bind(self).call(*args)
>>       end
>>     end
>>   end
>>end
> 
> Two questions of this solution.  (It works and is what I need now so
> I'm just looking to round out Ruby skills.)
> 
> 1 Why is  the 'remove_method(name)' line necessary?  Does not the next
> define_method call get rid of the method anyway by overriding?

Overriding methods usually produces warnings. It's best to remove the 
methods first.

> 2 The module requires use of 'extend' instead of 'include'.  Is there
> a comparable 'include' solution, and (if there is) would it be
> preferred because, for example, one could not use this solution on a
> class that already extends something else?

Actually, I think this is the cleanest solution. In theory you could 
also offer a custom append_features() which defines the methods on the 
class or module including Memoize itself. That's more complex and not as 
easy to understand, though, in my opinion.