From: Eric Wong <normalperson@...>
Date: 2012-05-10T05:48:00+09:00
Subject: Re: How to use Data_Wrap_Struct to assign the DATA VALUE to an exsiting Ruby object?

I単aki Baz Castillo <ibc@aliax.net> wrote:
> Hi, my code receives an arbitrary klass name (provided by the user)
> and I need to create an instance of such a klass and also wrap a C
> pointer within it.
> 
> Unfortunately Data_Wrap_Struct(VALUE class, void (*mark)(), void
> (*free)(), void *ptr") requires a class VALUE rather than a single
> object/instance. So I expect that I *cannot* attach/wrap a C DATA
> pointer into an *existing* Ruby object and, instead, I need to store
> the DATA pointer within an internal attribute of the object, am I
> right?

Ruby itself uses this idiom in some places:

	DATA_PTR(self) = ptr;

Seriously, the best way to learn C extensions is to read Ruby itself
(and its C extensions).