Just look for state-machine (finite state automata) on github

https://github.com/search?q=state-machine&type=repositories

This is a very common pattern in Ruby to manage state. It's especially useful to guard entering impossible states with respect to business logic and figuring out what went wrong. Something along the lines of:

    Can't transition Command from 'ordered' to 'to-deliver': paid() == false

look at this gem https://github.com/pluginaweek/state_machine to get an idea of what features are possible

Sum type is key, called "discriminated union" sometimes generally. In Rust this is an `enum`. Simulated in some languages as tuples with tag first element. Discrete number of states, attaching information only relevant to each single state. Thus, never have invalid combination of other fields.