From: James Britt <james_b@...>
Date: 2006-01-09T09:15:11+09:00
Subject: Re: Ideas on "Why Living Dangerous can be A Good Thing" in Ruby?

gwtmp01@mac.com wrote:
> 
> On Jan 8, 2006, at 5:47 PM, Steve Litt wrote:
> 
>> Personally, I'd NEVER gratuitously add a method or instance var to  a 
>> class at
>> runtime. If I needed more methods than the class provided, I'd  
>> subclass it.
> 
> 
> I'm not sure I follow this.  You think that subclassing at runtime is  
> better
> in some way than simply adding a method to a class? It is hard to  talk 
> about
> this stuff in the abstract.  For example, I feel differently about  
> dynamically
> adding methods to Array than I would to a class I created to solve a  
> particular
> problem.
> 
> I think it does take a certain amount of paradigm shifting to see  
> solutions to
> problems that involve dynamically creating methods in classes or on  
> particular
> objects.  Until you make that shift those facilities seem quite  abstract.
> 
> For example, in Rails you can call methods like:
> 
>     Model.find_by_date
>     Model.find_by_name
>     Model.find_by_city
>     Model.find_by_city_and_date
> 
> Those methods don't exist until you call them at which point they are  
> defined
> and added to the class.  

Really? I  thought they were simply reparsed by method_missing into 
messages of the form find( <assorted criteria>) asinvoked, not turned in 
"permanent" methods.  Interesting.

Which raises a question:  Is it metaprogramming if I use method_missing 
to parse messages, see if it can reformulate the message into a known, 
workable form, and then redispatch by invoking 'send'?  No code writing, 
no method adding.

Is that not simply the point of method_missing; i.e., it is simply a 
Ruby/OO idiom.  Messages need not map to methods.

And then isn't adding them as methods just an optimization technique to 
avoid the cost of calling method_missing on repeated invocations? It's 
memoization for behavior.

Is memoization metaprogramming, or is it only metaprogramming when 
behavior is altered?


James
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