From: Thomas Allen <thomasmallen@...>
Date: 2010-04-21T06:50:06+09:00
Subject: Proxying method calls

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

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

class B
    def b
        'b'
    end
end

require 'test/unit'

class MethodTest < Test::Unit::TestCase
    def setup
        @a = A.new
    end

    def test_method_missing
        assert_equal 'b', @a.b
        assert_raise NoMethodError do
            @a.c
        end
    end

    def test_respond_to
        assert @a.respond_to? :b
        assert_equal false, @a.respond_to?(:c)
    end
end

Thomas