The Classic Objections to Act Utilitarianism

Act utilitarianism says that the right act is which of those available to the agent would produce the most happiness or welfare. But suppose you're in a circumstance where actually you've promised me this money that's in your pocket, for example. That seems to be a flaw with act utilitarianism and so I prefer a version called rule utilitarianism. Rule utilitarianism says utility should be used to assess rules, but then rules should beused to assess acts.