string.c:2905
static VALUE
rb_f_chomp(argc, argv)
    int argc;
    VALUE *argv;
{
    VALUE str = uscore_get();
    VALUE dup = rb_str_dup(str);

    if (NIL_P(rb_str_chomp_bang(argc, argv, dup)))
	return str;
    rb_lastline_set(dup);
    return dup;
}
