hash.c:499
static enum st_retval
select_i(key, value, result)
    VALUE key, value, result;
{
    if (key == Qundef) return ST_CONTINUE;
    if (RTEST(rb_yield_values(2, key, value)))
	rb_ary_push(result, rb_assoc_new(key, value));
    return ST_CONTINUE;
}
