From: Rein Henrichs <reinh@...>
Date: 2010-06-15T08:10:07+09:00
Subject: Re: Do I overuse class methods?

On 2010-06-14 10:35:10 -0700, Michał Zając said:

> W dniu 2010-06-14 15:33, Robert Klemme pisze:
>> 
>> As a compromise Michael could use module Singleton and thus define
>> instance methods without the overhead of creating new instances all
>> the time.
>> 
> 
> I think this is interesting idea.
> I have spent much time in Java / C# environments with heavy use of 
> dependency injection pattern so maybe this is source of my aversion to 
> stateless classes manual instantiation - usually something else has 
> done it for me :D Using Singleton pattern is more similar to Service 
> Locator but it may be good alternative.
> 
> Thanks

Ruby's design patterns (in the Gang of Four sense) are extremely 
lightweight compared to their Java equivalents. Rick Olsen's Design 
Patterns in Ruby book shows good idiomatic Ruby implementations of the 
GoF patterns. That said, I don't think you want a Pattern at all. I 
think you want a more *object oriented* architecture.

IRT Singleton: I think that Singleton is just a way to cheat and get 
global state that looks like instances. I didn't present it as a 
solution because (imo) it's really just a restatement of the problem. I 
try to avoid it for the same reasons that I try to avoid the classes 
you're asking about. Let me put it this way: replace all of your 
pseudo-classes (these classes that don't instantiate and are used as 
singleton method holders) with this:

YourClass = Object.new

def YourClass.some_method
  ... do stuff ...
end

... more ...

This is functionally equivalent. Does this look like good Ruby code? Is 
this good OO design? If not, why not? The classes you're asking about 
aren't (functionally) classes at all: they're just objects like this 
one. You should object to them for the same reasons that you (may) 
object to the above.

Also, Ruby has far better mechanisms than dependency injection. So much 
so, in fact, that Rails core member and creator of two different Ruby 
dep. injection libraries, Jamis Buck, recently gave a great talk about 
why you don't need dependency injection in Ruby. Summary is here, and 
is a good read if you're coming from heavy, "enterprisey" languages 
like Java: 
http://weblog.jamisbuck.org/2008/11/9/legos-play-doh-and-programming.

Coming from a Java background, the best thing you can do is let go of 
the heavy pattern-driven architectures that are common in 
enterprise-land (the ServiceLocator, CachedTemplateFactoryProxyFactory, 
whatever) and enjoy the freedom of working with simple, lightweight 
classes and objects.

-- 
Rein Henrichs
http://puppetlabs.com
http://reinh.com