Use here_document with `class_eval` to simplify debugging:

```ruby
class_eval <<-"end_eval", __FILE__, __LINE__

  def #{block_accessor}(*args, &block)
    unless args.empty? && block.nil?
      args.push block if block_given?
      @#{block_accessor} = [args].flatten
    end

    @#{block_accessor}
  end

end_eval
```

[`class_eval`](http://www.ruby-doc.org/core-2.1.5/Module.html#method-i-class_eval) (as well as `module_eval` and some other methods) actually takes blocks _or strings_ for evaluation, so instead of passing a block, we pass everything as a [here-document](http://en.wikipedia.org/wiki/Here_document#Ruby) string, and add two additional params for filename and line in that file. 

When exception hits the fan, it will be trivial to locate.