From: ara.t.howard@...
Date: 2006-09-21T23:11:12+09:00
Subject: Re: Assistance wanted for integrating existing C-API into Ruby

On Thu, 21 Sep 2006, Feurio wrote:

> Hello,
>
> I am seeking assistance for writing a ruby wrapper for the c-api of an
> existing enterprise system. This job is a paid job.
>
>
> In my vision the access from ruby/rails to this existing system should be
> like working with active record.  Basically I think there should be a ruby
> layer to make the c-api accessible and another that integrates it with
> Active Record. I think this makes sense because my main focus is to access
> the data of the enterprise system.
>
>
> For the first layer I can imagine to use SWIG (this seems to be a good way
> to integrate a c-api from ruby; but if you know a better way just tell me)

if the api is simple, or even moderately simple, you may be able to wrap it
this afternoon using ruby/dl - which allows one to call c functions
__directly__ from ruby without any glue (swig) code.

here's an example which calls atoi(3):

     harp:~ > cat a.rb
     require "dl/import"
     require "dl/struct"

     module LIBC
       extend DL::Importable
       begin
         dlload "libc.so.6"
       rescue
         dlload "libc.so.5"
       end
       extern "int atoi(char*)"
     end

     p LIBC.atoi("42")


     harp:~ > ruby a.rb
     42

if you take this approach you'd probably be best off doing something like

   one_to_one_mapping_of_c_to_ruby = Module.new{
     #
     # as the example above
     #
   }.unit_test!

then

   high_level_interface = Module.new{
     #
     # use one_to_one_mapping_of_c_to_ruby to provide high level functions
     #
   }.unit_test!

swig is a fine peice of software but, sometimes, there's no need to actually
write/generate an extension.

kind regards.

-a
-- 
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei