From: Luigi Ballabio <ballabio@...>
Date: 2002-04-05T00:42:14+09:00
Subject: Re: Help: Ruby<->C++ callbacks


Guy,
	thanks a lot for the reply.
The scaffolding is not a big problem: I'm using SWIG to export the stuff, 
so the class destructor is automatically passed to Data_[Wrap|Make]_Struct 
as the mark function, so I can put there a call to rb_gc_mark for the proc.

What I'm concerned about is the following scenario:

// the Callback constructor makes a copy of the VALUE pointing to
// the proc and stores it away, but the Ruby interpreter doesn't know.
irb> c = Callback.new(proc { puts "Hello World!" })

// for all I know, here the interpreter could decide to gc the
// proc object since the only reference that it saw is already
// out of scope

// therefore, the following call could try to use a pointer to
// a gc'ed object and fail spectacularly.
irb> c.doit
Goodbye, cruel world.

The question really was, how do I tell the interpreter that I'm holding a 
reference to a Ruby object from C++?

Thanks again,
		Luigi