From: Ryan Davis <ryand-ruby@...>
Date: 2007-07-17T07:53:25+09:00
Subject: Re: C library extension question


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.