To find out later that not everything can be cached, e.g. time(), rand(), file_get_contents()... to find out further that no sys or lib call that contains I/O c

To find out later that not everything can be cached, e.g. time(), rand(), file_get_contents()... to find out further that no sys or lib call that contains I/O can be cached. And then damn it, why bother caching at all?