From: emilie3012@... (Steve Hart)
Date: 2003-04-10T11:42:27+09:00
Subject: Re: tutorial on embedding ruby (review)

ptkwt@shell1.aracnet.com (Phil Tomson) wrote in message news:<b7251v087t@enews3.newsguy.com>...
> In article <200304092336.07600.armin@xss.de>,
> Armin Roehrl  <armin@xss.de> wrote:
> >> http://metaeditor.sourceforge.net/embed/
> >Figure 3 alone is one reason to look at it.
> >http://metaeditor.sourceforge.net/embed/cleanup.png
> >
> 
> Figure 4 is pretty cool too.
> 
> I'm going to have to take a look at this part:
> "Most people think that SWIG can be used ONLY for ruby extensions. But if 
> you are clever you can actual use it for embedding. "
> 
> Phil

Hi Simon,

I'm in the middle of embedding ruby into a c++ project and read the
tutorial with interest. It's great to see something out there that
addresses this issue. I've already emailed you with some specific
questions but forgot to add commenst for the tutorial.I'm a newcomer
to ruby and swig so any info is great to see
So some points that I would find usefull would be:

1) A more detailed explanation of THE GC interaction would be good. I'
not sure if you need to do both marking and rb_global_variable and/or
rb_gc_register_address. If I call rb_ary_new2 in my C code should I
always inform the GC? I understand that I need to use a mark function
for wrapped c classes but where do I get the VALUE from to pass to the
mark function?
If I am marking and object correctly what do I do when I want to free
it off - just stop marking? The example given under 'speed issues'
protects the object list (using rb_gc_register_address) but what do I
do if I want to free of just some of the objects in the list?. Also,
what happend if the GC runs between 		objects = rb_ary_new() and
rb_gc_register_address(&objects); ? Or can this never happen.

2) An example explaining finializers would be nice - still not sure if
I need them. Since I'm probably what Matz would describe as a 'normal'
user perhaps I should stear clear!.

3) rb_require over rb_load_protect - I started off using rb_require
but then found that if rb_require fails with a script error and I then
corrected the script re re-rb_requiring ignored the changes - I assume
the script is cached. Switching to rb_load_protect reloads the script
each time - but is this correct? What does the second argument to
rb_load_protect do

3) More detail for the swig version - especially for the case when a
ruby class inherits a swigged up c class and you need to pass a
swigged up c class instance throug to it and then back out again

e.g.
c++:

SwigClass1 *sg = new SwigClass1();
sgValue = Data_Wrap_Struct(rb_path2class("MyModule::SwigClass1"),0,0,(void
*)sg);

oClass = rb_const_get(rb_cObject, rb_intern("SwigClass2"));
oObj = rb_funcall(oClass, rb_intern("new"), 1,sgValue);

ruby:

class MyClass < MyModule::SwigClass2
   def initialize(swigClassValue)
      super(swigClassValue)
   end
end


4) Also under speed issues - should'nt void mystruct_alloc(VALUE
klass) return VALUE?

All this is, of course, relevant to me at the moment and I don't
expect answers (well, some would be nice) but I hope it helps. I'm new
to newsgroups too so I don't even know what all the arreviations and
smiley colons mean yet!
Cheers
Steve