io.c:2737
static VALUE
rb_obj_display(argc, argv, self)
    int argc;
    VALUE *argv;
    VALUE self;
{
    VALUE out;

    if (rb_scan_args(argc, argv, "01", &out) == 0) {
	out = rb_stdout;
    }

    rb_io_write(out, self);

    return Qnil;
}
