From: Jason Voegele <jason@...>
Date: 2002-05-02T04:03:11+09:00
Subject: Scope of Singleton Classes

I'm writing an object proxy that intercepts method calls with method_missing
and then forwards them to another object for handling.  I want to avoid the
overhead of using method_missing every time, so I'd like to define a new
method each time method_missing is invoked that actually does the
forwarding.  I have a few questions about this approach.

I tried something like this:

class ObjectProxy
    def method_missing(operation, *args)
        class << self
            define_method(operation, args) do |opargs|
                forward(*opargs)
            end
        end
    end

    def forward(operation, *args)
        # call operation on target object
    end
end

1) I was surprised to learn that the singleton class defined by "class <<
self" does not have access to local variables in its lexical scope (e.g.
"operation" and "args").  Is this by design?

2) Is there solution that utilizes define_method rather than eval?

3) Is caching methods like this (rather than relying on method_missing for
each invocation) a significant enough performance improvement to make it
worth it?

Thanks,
-- 
Jason Voegele
"We believe that we invent symbols. The truth is that they invent us."
    -- Gene Wolfe, The Shadow of the Torturer