Ruby Forum Ruby > ruby callback for a SWIG wrapped C function

Hello list!

I successfully wrapped using swig a library I wrote in ruby, all its 
simple
functions works very well.
I said simple because I have a function that takes a callback function 
as
argument, and I look for the way how to give a pure ruby callback 
function
as argument of this function wrapped by SWIG!

By the way, may I meet problems if some of my functions uses the
"callback-needing" function inside of them?

Than kyou

Lyes Amazouz wrote:

> I said simple because I have a function that takes a callback function as
> argument, and I look for the way how to give a pure ruby callback function
> as argument of this function wrapped by SWIG

You haven't supplied enough detail to provide specific advice so you'll
need to adapt what follows. A generally effective way of dealing with
this is in SWIG to do something like:

1. Create a short 'bridging' function in C that converts arguments to
ruby and then calls rb_yield

Let's say your callback function is expected to take a single int
argument and returns void. Put this is in as a SWIG literal in your .i 
file.

%{
void DoYielding(int arg_1)
{
   VALUE rb_arg_1 = INT2NUM(arg_1);
   rb_yield(arg_1);
}
%}

If the callback needs to return a value, you'll need to capture the
return value of rb_yield and do some Ruby -> C type translation.

2. Set it up so that method calls in ruby to the original
callback-needing function supply this callback as the C argument

If the callback-needing function needs to accept a single int parameter,
the method that is exposed in ruby will look something like

VALUE method_needing_callback(VALUE rb_input_arg)
{
   int input_arg = NUM2INT(rb_input_arg);
   C_Function_Needing_Callback(input_arg, &DoYielding);
   return Qnil;
}

Then do whatever you need to get this function mapped to a ruby method,
using normal SWIG techniques.

3. Compile, and call the method with a block

some_object.method_needing_callback(42) do | an_int |
   puts "The callback was called with argument %i" % an_int
end

> By the way, may I meet problems if some of my functions uses the
> "callback-needing" function inside of them?

Not if you do it right. You can still call the callback-needing function
with a normal callback, written in pure C/C++.

a

On Wed, Aug 20, 2008 at 12:06 PM, Alex Fenton 
<alex@deleteme.pressure.to>wrote:

>
>  rb_yield(arg_1);
> the method that is exposed in ruby will look something like
>
> Not if you do it right. You can still call the callback-needing function
> with a normal callback, written in pure C/C++.
>
> a
>

Thank tou for the Reply, I'll try what you  suggested me. If I have more
troubles, I will repost another message