gistfile1.rb

# robgleeson's fork much improved

class ErrorDelegate

  attr_reader :pointer
  alias_method :to_pointer, :pointer

  def initialize
    @pointer = Pointer.new_with_type '@'
  end

  def method_missing method, *args
    @pointer[0].send method, *args
  end

end

error = ErrorDelegate.new
document = NSXMLDocument.alloc.initWithData '<?xml version="1.0" encoding="UTF-8"?>',
                                             options: 1 << 9,
                                             error: error.to_pointer

p error.localizedDescription