A Ruby extension that will allow access to instance variables that are set in C and do not begin with an "@".

extconf.rb

require 'mkmf'

have_header('ruby.h') or missing('ruby.h')

dir_config("ivar")

create_makefile("ivar")

irb.sh

ruby extconf.rb && make && irb -I . -r ivar

ivar.c

#include "ruby.h"

static VALUE rb_mIvar;

static VALUE rb_ivar_iv_get(VALUE self, VALUE key) {
  return rb_ivar_get(self, rb_to_id(key));
}

static VALUE rb_ivar_iv_set(VALUE self, VALUE key, VALUE value) {
  return rb_ivar_set(self, rb_to_id(key), value);
}

void Init_ivar() {

  rb_mIvar = rb_define_module("Ivar");
  rb_define_method(rb_mIvar, "ivar_get", rb_ivar_iv_get, 1);
  rb_define_method(rb_mIvar, "ivar_set", rb_ivar_iv_set, 2);

}

usage.rb

$:.unshift('.')
require 'ivar'

Object.send(:include, Ivar)

e = StandardError.new("foo")

puts "Error message is: #{e.message}"

e.ivar_set(:mesg, "bar")

puts "Error message is: #{e.message}"