From: Jason Roelofs <jameskilton@...>
Date: 2008-12-12T01:52:29+09:00
Subject: Re: Q: FFI and C++?

On Thu, Dec 11, 2008 at 11:28 AM, Jeremy Henty <onepoint@starurchin.org> wrote:
> On 2008-12-11, Jason Roelofs <jameskilton@gmail.com> wrote:
>
>> Because of the  complexity that C++ adds, I  doubt that any feasible
>> FFI library can be made that works reliably against C++ libraries,
>
> I was afraid of that.
>
>> Rice - ...
>> Rb++ - ...
>
> I looked at  those but I thought they were  targeted at generating MRI
> bindings.  The point of using FFI is to eliminate MRI-specific C code.
> I just need to wrap C++ with C to get functions that FFI can call, eg.
>
>    extern "C" {
>
>    void *thing_new() { return new Thing(); }
>    void thing_delete(void *vt) { delete (Thing *) vt; }
>    void *thing_bar(void *vt) { return ((Thing *) vt)->bar(); }
>
>    // etc. etc. etc.
>    }
>
> I already know this works, now I'm trying to save effort, particularly
> with parsing C++  and autogenerating wrapper code.  Maybe  I could use
> rbgccxml and  add my  own XML  -> wrapper code  backend.  It  looks as
> though rbgccxml is  precisely the bit of rbplusplus  that I would want
> to reuse.
>
> Thanks for your help,
>
> Jeremy Henty
>
>

I'd ask that if you already need to write and compile a wrapper to
make a library work with FFI, then why bother with FFI in the first
place? Rice / Rb++ will get you a lot farther in less time than trying
to hack your way into using the FFI library, besides the fact that
your sample wrapper code will wreck complete havok with your C++ <->
Ruby type mapping, requiring a lot more code to handle converting
types to and fro as needed. Rice gives you all this automatically.

In short, Rice isn't about generating MRI bindings for you but more
about exposing an OO wrapper around the MRI bindings, so you don't
have to get into the nitty-gritty details of Ruby's C API, and then
Rb++ sits on top of that to auto-generate as much Rice code as
possible so you only have to work in Ruby.

Jason