From: Oliver <fwang2@...>
Date: 2007-07-17T08:50:32+09:00
Subject: Re: C library extension question

Thanks for the suggestion, I will take a look at the sample lib you
suggested.
However, I don't fully understand the reasoning of "not wrapping it".

Here is my line of thinking:

- the original C function register() expects an array of function
pointers, and those functions are suppose to be user-supplied and
implemented by C.

- Ideally, we should now allow those functions to be implemented by
ruby ... is this possible at all?

thanks

Oliver


On Jul 16, 6:53 pm, Ryan Davis <ryand-r...@zenspider.com> wrote:
> On Jul 16, 2007, at 12:20 , Oliver wrote:
>
> > /* command dispatch structure */
> > typedef int (*proxy_cmd)(int trans_id, int nargs, char **args);
>
> > struct proxy_commands {
> >         int                      cmd_base;
> >         int                      cmd_size;
> >         proxy_cmd *      cmd_funcs;
> > };
> > typedef struct proxy_commands   proxy_commands;
>
> What you're looking for is probably Data_Wrap_Struct and friends. See
> ruby.h and intern.h. For a simple example of this in action, look at
> the image_science.rb code (available via gems or on the seattlerb
> project on rubyforge). It is only 228 lines long currently so it is a
> pretty easy read.
>
>
>
> > Then, as a user you can define an array of function pointers like
> > this:
>
> > proxy_cmd cmds[] = {
> >    func_a,
> >    func_b,
> >    func_c,
> >    ...
> > };
>
> > and fill in the structure:
>
> > proxy_commands mytabs = {
> >     CMD_BASE;
> >     sizeof(cmds)/sizeof(proxy_cmd),
> >     cmds
> > }
>
> I'd suggest using a ruby array at this stage. Cleaner.
>
> > An example of API will look like this:
> > register(&mytabs, .... )
>
> > What is the best way of wrapping this in Ruby?
>
> Well, the BEST way is to not wrap it at all:
>
> def func_a; ...; end
> def func_b; ...; end
>
> msgs = [:func_a, :func_b]
>
> msgs.each do |msg|
>    send msg
> end
>
> Short of that, you'll want to poke around with DataWrapStruct.