From: ts <decoux@...>
Date: 2002-04-05T01:01:01+09:00
Subject: Re: Help: Ruby<->C++ callbacks

>>>>> "L" == Luigi Ballabio <ballabio@mac.com> writes:

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

 Well, here you return an object with its mark and free function

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

 No. When the GC run it will mark all alive objects. This mean that it will
 mark the variable `c' (`c' is still in scope) and to do this it call the
 mark function that you have given in Data_Wrap_Struct. Because your mark
 function call rb_gc_mark() on the Proc object, the GC will not try to
 remove it (i.e. the Proc object is still alive for the GC) 

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

 You just define a mark function (given to Data_Wrap_Struct) and in this
 mark function you call rb_gc_mark() on all ruby object holding by C++



Guy Decoux