gistfile1.rb

class HouseDetail
  def foo
    return [1,2,3]
  end
end

class KeyInvoker

  instance_methods.reject {|meth| meth.to_s =~ /^_/ }.each { |meth| undef_method(meth.to_sym) }

  def initialize(object)
    @proxy_object = object
  end

  def call(path)
    path_elements = path.split(".")
    meth, path = path_elements.shift, path_elements.join('.')
    value = __send__(meth)
    if path_elements.empty?
      respond_to?(meth) ? value : nil
    else
      KeyInvoker.new(value).call(path)
    end
  end

  def respond_to?(meth)
    @proxy_object.respond_to?(meth)
  end

  def method_missing(meth, *args, &blk)
    if @proxy_object.respond_to?(meth)
      @proxy_object.send(meth)
    else
      @proxy_object
    end
  end
end

ki = KeyInvoker.new(HouseDetail.new)
puts ki.call("house_detail.foo.length.to_s")
puts ki.call("house_detail.foo2.length")
puts ki.call("house_detail2.foo.length")
puts ki.call("house_detail.foo.length3")