From: George Ogata <george.ogata@...>
Date: 2006-12-16T11:18:11+09:00
Subject: Re: method_missing question

On 12/15/06, Peter Szinek <peter@rubyrailways.com> wrote:
> Now, the problem is I would like to write the above example like this:
>
> book do
>   title
>   price
> end
>
> i.e. without the Ps.
> P's sole purpose is to define method_missing - I did not want to
> override Object.method_missing since I would like to release this code
> to the wild and I think it could collide with my potential future user's
> Object.method_missing.
>
> I have then experimented with modules (mimicking namespace
> functionality) but that still did not provide the possibility to omit
> the class name. I would need something equivalent to include - you can
> omit the module name if you include the module - but with classes.
>
> I have no idea if this is possible in Ruby, but is there something like
> run this code in a different context or something?

Hi Peter,

This sort of thing probably already exists somewhere, but I don't know
what it's called.  (The 'script' that Michael mentioned looks like
something else to me... ?)

So anyway, here's a starting point.  The trick is to use instance_eval
to change the value of 'self' within the block.

class Node
  # Rename all existing methods to start with '__', so they're not
  # likely to collide with your attribute names.  We'll leave some
  # methods alone, since they're necessary for some basic operations.
  methods = (instance_methods + private_instance_methods)
  methods = methods - %w'__send__ __id__ initialize inspect'
  methods.each{|m| alias_method("__#{m}", m); undef_method(m)}

  def method_missing(*args, &block)
    key, val = *args
    if block
      args.length == 1 or
        raise ArgumentError, "value and block given"
      node = Node.new
      __instance_variable_set("@#{key}", node)
      node.__instance_eval(&block)
      return node
    else
      args.length <= 2 or
        raise ArgumentError, "too many arguments"
      if args.length > 1
        __instance_variable_set("@#{key}", val)
      end
      return __instance_variable_get("@#{key}")
    end
  end
end


### Usage

node = Node.new
node.root do
  a 1
  b 2
  c do
    d 3
    e 4
  end
end
p node.root.c.d  #=> 3
p node.root.c    #=> #<Node:0xb7dd55c4 @d=3, @e=4>
p node           #=> #<Node:0xb7ddb8ac @root=#<Node:...>>