From: Stefano Crocco <stefano.crocco@...>
Date: 2007-05-21T21:02:59+09:00
Subject: Re: Simple Q: object creation to be determined by incoming data

Alle luned� 21 maggio 2007, Todd Benson ha scritto:
> I'm almost embarrassed to ask this, because I'm bound to be pointed to some
> code that I've almost certainly read already, but here goes my ruby newbie
> question:
>
> I have an incoming stream of data in separated chunks, each having a
> beginning word that defines that chunk's place in the world (how it will
> respond to #to_s, etc).  Currently, I model each chunk as an object; each
> has its own class.  Basically, I'm unserializing object data, but I provide
> the object functionality.  I want to do off-the-stream object creation, and
> so I've went and done something like:
>
> instance_eval( "#{class_name_from_stream_chunk}.new( data_from_stream_chunk
> )" )
>
> Is this the only way to do this (by "way", I mean the code and also the
> manner), and if not, the best way?

I'm not sure I understand correctly your question. I think you don't need to 
use instance eval. If class_name_from_stream_chunk is a string/symbol and the 
class is defined in the module M (if it is defined top level, substitute M 
with Kernel), you can do:

M.const_get(class_name_from_stream_chunk).new(data_from_stream_chunk)

You can also define a method which wraps this in a simpler interface:

def M.new_from_chunk name, data
  const_get(name).new(data)
end

and use it this way:

res = M.new(class_name_from_stream_chunk, data_from_stream_chunk)

I hope this helps

Stefano