From: ara.t.howard@...
Date: 2006-07-18T02:08:14+09:00
Subject: Re: Save me from the method_missing

On Tue, 18 Jul 2006 transfire@gmail.com wrote:

> Yes, I do constrain the config keys to single word case insensitive strings.
> Unfortuate I just don't see a nicer way. "y[:a][:b][:c]" just lacks all
> elegance. And path notation (y/:a/:b/:c) while a _little_ better can't use
> setting at the end (eg. y/:a/:b/:c = x). So what else is there?

brainstorming:



harp:~ > cat a.rb
require 'yaml'

class Config < ::Hash
   def self.new(yml) super().update YAML.load(yml.to_s) end
end
def Config(*a, &b) Config.new(*a, &b) end


c =
   Config %(
     a:
       b:
         c: 42
   )


#
# just an idea
#
   class Config < ::Hash
     def munge_keys *keys
       keys.compact!
       keys.flatten!
       keys.map!{|key| key.to_s.strip.split %r/\s/}
       keys
     end
     def [] *keys
       keys = munge_keys keys
       h = self
       nil while Hash === (h = h.fetch keys.shift.to_s)
       h
     end
     def []= *argv
       v, keys = argv.pop, argv
       keys = munge_keys keys
       h, h2, k = self, nil, nil
       h = h2 while Hash === (h2 = h.fetch(k = keys.shift.to_s))
       h[k] = v
     end
   end

   p c[ :a, :b, :c ]

   c[ :a, :b, :c ] = 'forty-two'

   p c[ :a, :b, :c ]

   p c

#
# another, sillier one
#
   class Config
     alias_method '^', '[]'
   end

   p c ^ %w( a b c )



harp:~ > ruby a.rb
42
"forty-two"
{"a"=>{"b"=>{"c"=>"forty-two"}}}
"forty-two"

>> what do you mean 'iffy' exactly?
>
> Well, for instance. If a public method is added to Kernel or Object (or
> any subclass for that matter) it will show up in ones class and block
> out method_missing.

i see three ways to get around this:


   a) use block form methods

       obj.configure{

         # push method_missing handler and dsl methods onto stack

         # instance_eval the block

         # pop them off

       }

     so

       obj.configure{
         a 4
         b 2
       }

     this gives you a chance to 'clean-out' the obj each time.


   b) use block form with blank slate proxy

     obj.configure{
       # setup blank-slate proxy

       # instance_eval the block on proxy!

       # copy all state from proxy into object
     }


   c) use block form with an easily identifiable method name.  i do this in my
   xx html/xml generation lib where

     puts xhtml_{

       p_{ 'note that the "p" tag works! }

       b_{ i_{ u_{ "bold-italic-underline } } }

     }

   i can filter __only__ those methods ending in '_'.  this has many
   advantages:

     - easy to distiguish ruby's methods like 'p' from html methods like 'p_'

     - easy to grep for 'special' methods in you source.


i realize none of these really apply to a config style class.

>
>> that the list of 'require' methods seems to change every few months?
>
> Not sure what you mean.

gsub/require/required/

meaning __id__, __send__, et al.


cheers.

-a
-- 
suffering increases your inner strength.  also, the wishing for suffering
makes the suffering disappear.
- h.h. the 14th dali lama