From: Daniel Berger <djberg96@...>
Date: 2006-10-31T02:10:14+09:00
Subject: Re: Alias singleton method from C

Tim Pease wrote:
> On 10/30/06, Daniel Berger <djberg96@gmail.com> wrote:
> >
> > Good question.  I'm not sure why this code fails:
> >
> > #include <ruby.h>
> >
> > static VALUE foo_bar(){
> >    return rb_str_new2("hello");
> > }
> >
> > void Init_foo(){
> >    VALUE cFoo, singleton;
> >
> >    cFoo = rb_define_class("Foo", rb_cObject);
> >
> >    rb_define_singleton_method(cFoo, "bar", foo_bar, 0);
> >
> >    singleton = rb_const_get(rb_cObject, rb_intern("Foo"));
> >    rb_define_alias(singleton, "baz", "bar");
> > }
> >
> > When I compile and run that it fails with "undefined method `bar' for
> > class `Foo'" even though it clearly is defined.  I can see in class.c
> > that rb_define_alias is just calling rb_alias from eval.c.  It looks
> > like rb_alias handles singletons differently, but why it's not working
> > in the example I provided I'm not sure.
> >
>
> rb_define_alias only works for instance methods.

It should work for either singletons or instance methods.  If it
didn't, then this code wouldn't work:

class Foo
   class << self
      def bar
         "hello"
      end
      alias baz bar
   end
end

p Foo.bar => "hello"
p Foo.baz => "hello"

The C example I pasted is meant to do what I've done there.

Internally rb_define_alias calls rb_alias (in eval.c) which checks to
see if klass is a singleton or not.  So, in theory, I should be able to
do:

rb_define_alias(singleton, baz, bar);

But obviously I'm doing something wrong - I'm just not sure what.

Regards,

Dan

PS - A rb_define_singleton_alias() would be a handy function. :)