From: Laurent Julliard <Laurent.Julliard@...>
Date: 2002-02-18T03:24:45+09:00
Subject: Accessing C structure members from Ruby

I'm in the process of writing a Ruby Extension for a C library. This C 
library has a number of C structures which I'm going to use as a basis 
to create the corresponding Ruby Classes. So far so good.

However instead of just using the Data_Wrap_Struct  facility to 
encompass these structures I'd like to put in place a mechanism where 
each member of the original C structure has an equivalent instance 
variable in the corresponding Ruby Class. What is the best way to do this?

I see two complementary approach for the moment but may be you'll have 
other ideas/tips:

1) I can put in place a copy mechanism in the C extension so that 
whenever a method is called it copies all the instance variables in the 
corresponding C structure members, call the C function, and copy the C 
struct members back to the Ruby instance variables when the C function 
returns.

2) In addition I could also define Ruby accessors (Get/Set) which are 
small C function which write to/ read from the appropriate C strcture 
member. I saw the rb_define_attr fucntion but unfortunately it looks 
like there is no way to hook accessors to "virtual" instance variables 
that would be actually be stored in C structure member. Am I missing 
something here?

All comment/suggestion welcome.

Laurent