From: Robert Klemme <shortcutter@...>
Date: 2010-04-22T01:25:07+09:00
Subject: Re: Proxying method calls

On 04/20/2010 11:48 PM, Thomas Allen wrote:
> How do I safely proxy method calls from one class to another, as a
> fallback for when the main class doesn't respond to the call in
> question? Is my implementation of respond_to? and method_missing below
> correct (passing tests at bottom)?
> 
> class A
>     def initialize
>         @b = B.new
>     end
> 
>     def respond_to? call
>         unless super call
>             @b.respond_to? call
>         end
>     end

I am wary about respond_to? - usually I would not bother to override 
this.  The reason is that there is no guarantee that an object really 
responds to the method if respond_to? returns "true" - and the other way 
round.

>     def method_missing call
>         if @b.respond_to? call
>             @b.send call
>         else
>             super
>         end
>     end

There is at least one issue: you do not propagate method arguments 
properly.  Better do

     def method_missing(*args, &block)
       @b.send(*args, &block)
     end

Delegating to super is only necessary if the super class also implements 
method_missing.  Otherwise you'll get an exception from @b anyway.

Please see also classes Delegator and SimpleDelegator.
http://ruby-doc.org/stdlib/libdoc/delegate/rdoc/index.html

Kind regards

	robert


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