From: Tobias Grimm <listaccount@...>
Date: 2004-08-21T07:37:11+09:00
Subject: Re: Overriding virtual C++ method in Ruby

Lyle Johnson wrote:

> Please read up on SWIG's cross-language polymorphism feature (a.k.a.
> the "directors" feature), described here:

Thanks for the hint, I missed this. But when enabling the directors feature
some errors are raised.

Very simple example:

[foo.cc]
class Foo
{
     public:
         virtual char *test(void)
         {
             return "C++ implementation";
         }
         virtual ~Foo() {};
};


[foo.i]
%module(directors="1") ModFoo

%feature("director") Foo;

%include "foo.cc"


[bar.rb]
class Bar < ModFoo::Foo
     def test
         p "ruby implementation of test called"
         return "Ruby Implementation"
     end
end

$foo2 = Bar.new


[main.cc]
int main()
{
     int state;

     ruby_init();
     ruby_init_loadpath();
     SWIG_init();

     rb_load_protect(rb_str_new2("bar.rb"), Qfalse, &state);
     checkRubyError(state);

     Foo *foo1 = new Foo();
     Foo *foo2;
 

     VALUE obj = rb_eval_string_protect("$foo2", &state);
     checkRubyError(state);

     rb_p(obj);

     Data_Get_Struct(obj, Foo, foo2);

     cout << "calling C++ implementation : " << foo1->test() << endl;
     cout << "calling Ruby implementation: " << foo2->test() << endl;

     ruby_finalize();
     return 0;
}

[Output - directors feature disabled]
#<Bar:0x402c5db8>
calling C++ implementation : C++ implementation
calling Ruby implementation: C++ implementation

[Output - directors feature enabled]
#<Bar:0x402c5c8c>
calling C++ implementation : C++ implementation
"ruby implementation of test called"
(eval): wrong argument type String (expected Data) (TypeError)
(eval): [BUG] Segmentation fault
ruby 1.8.1 (2004-02-03) [i386-linux]

Where can the problem be? the test() implementation of the Ruby Bar-class gets 
called, but then something seems to go wrong with returning the string value.

Tobias