From: Joel VanderWerf <vjoel@...>
Date: 2004-11-16T03:33:21+09:00
Subject: Re: [ANN] MinDI: Minimalist Dependency Injection

Avi Bryant wrote:
> Joel VanderWerf <vjoel@PATH.Berkeley.EDU> wrote:
> 
> 
>>The example from Jim Weirich's article would look like this in MinDI:
>>
>>   class JWApplicationContainer
>>     extend MinDI::Container
>>
>>     logfilename { "logfile.log" }
> 
> 
>>     quotes        { StockQuotes.new(error_handler, logger) }
> 
> 
>>   end
> 
> 
> Forgive me for being dense, but once you've gone this far, is there
> any particular reason not to simply write:
> 
> class JWApplicationContainer
>   def logfilename() "logfile.log"; end
>   
>   ...
> 
>   def quotes
>      @quotes ||= StockQuotes.new(error_handler, logger)
>   end
> 
>   ...
> end
> 
> and so on?  I think the win in simplicity probably outweighs the extra
> few characters you have to type...

I forgive you :) That reaction was exactly the initial reaction that DI 
provoked in me and which I wrote up in [ruby-talk:120214]. The style 
that you suggest is what I've used in my own code, and it took Jim's 
article to see that it was really a form of DI.

I'm not yet sure whether a more explicit DI (Arrow, or MinDI) will 
replace that style for me--I haven't actually used it in an application. 
It probably depends on how much I use the other service models besides 
singleton (e.g., #quotes, above) and prototype (#logfilename, in the way 
you defined it). In that case, DI may be a useful abstraction layer that 
saves more than typing.