The advice is that state is hard to deal with, so you should try to isolate it from the rest of your program. You can even organize stateful components like a c

The advice is that state is hard to deal with, so you should try to isolate it from the rest of your program. You can even organize stateful components like a cache to isolate the stateful components. - Make your stateful components "dumb". The cache should just have dumb put,get,delete methods. - Make your "smart" components stateless. Your component deciding which items to cache or remove or invalidate should be passed all the state they need to make their decisions as immutable parameters. This will make your lifecycle management code much easier to test or log. - Keep the part gluing the dumb state and the smart functions small In the end you still have a stateful component, but as a whole it should be easier to work with. For example, it's much easier to test time-based lifecycle decisions if you pass in the current time than if the component grabs the current time from your system clock.