How do you know when you're ready to date again?

A friend and I were talking about this. After you had broken up with someone (that you truly loved), how did you know that you were ready to start dating again? And, that you truly weren’t just wanting to fill that ‘void’ or that space in your heart that your ex once filled? And, if you still have feelings for your ex (despite the fact that more than likely you’ll never get back together), I’m guessing the answer is “no, you shouldn’t be dating, then”, right?