From: Joel VanderWerf <vjoel@...>
Date: 2007-09-23T05:19:37+09:00
Subject: Re: [ANN] CplusRuby - Gluing C and Ruby

Michael Neumann wrote:
> In the example you give I only see one minor difference. In CplusRuby, 
> method :stimulate can be called directly from the C-side, without 
> NUM2DBL conversions of Ruby-types. That's very important for my
> usage scenario.
> But I think you can do the same with cgen.

Actually, I don't think cgen has that feature.... one of the things I'll 
have to er, borrow, from cplusruby. Currently the only way to do this is 
to define a separate C function that the method calls.

Reading the cplusruby .c output, it looks like there is an outer 
function (Neuron_call__stimulate) that accepts ruby value arguments, and 
then converts them and calls an inner function (Neuron__stimulate), 
which expects C-typed arguments. You could do this in cgen by using 
define_c_method to define the outer function and define_c_function to 
define the inner function.

I guess I was used to performing the conversion manually, so I never 
added that feature as a convenience. I can see that it would be more of 
a necessity than a convenience if the function needed to be called from 
C as well as ruby.

The selfc->stimulate function pointer is another difference, and 
necessary for the same reason, I guess. In a cshadow struct, this struct 
member doesn't exist, but there is reference ("VALUE self;") back to the 
original object, on which you can call methods (with the additional 
friction of type conversions, if the caller is native C code).

The fact that you have pointers to functions that accept C-typed args 
makes access from C easy and efficient, but it also uses a lot of space 
in the struct with a pointer to each function that implements a method. 
What about having a unique struct for each class that keeps these 
pointers, and then the struct only needs a pointer to this "singleton"?

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407