From: Joel VanderWerf <vjoel@...>
Date: 2007-06-09T07:29:39+09:00
Subject: Re: Disadvantages of Dependency Inversion?

Peter Booth wrote:
> Given this, I'd say the drawbacks of DI are:
> 
> uncertain value proposition
> less explicit than the ServiceLocater pattern and thus harder to 
> debug/comprehend
> not a fit for Ruby
> canonical implementation (Spring) is a bit fat and overcomplex
> other Java implementations are sparsely documented and have uncertain 
> viability
> not pragmatic

It's pretty easy to build a lightweight DI framework in ruby, taking 
advantage dynamic language features like method_missing.[1]

But I rarely find the need to use it, even in relatively complex programs.

However, ruby has some DI-like idioms that are very useful, with no need 
for a framework. A somewhat imaginary variant on a very common example:

class Foo

   # map host to addr
   def addr_map
     @addr_map ||= {}
   end

   def session
     @session ||= Hash.new do |hsh,host|
       hsh[host] = Session.new(addr_map[host])
     end
   end

   def send_to_host(msg, host)
     session[host].send(msg)
   end

end


[1]  For example:

http://raa.ruby-lang.org/project/mindi/

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407