Conditional state transition

[dudycz]

Is there any possibility to make conditional transition that based on current machine state and input (event) data makes decision whether to transit to NextState or OtherState?

#[state]
pub enum ProcessState {
Init,
NextState,
OtherState,
Finished,
}

[eboody]

Yes! I'm actually working on a complete rewrite of statum so I'll re-respond to this once I have it worked out :) thanks for your issue!

[eboody]

Short answer: yes, but you do it by branching in a normal method and calling explicit transitions.

A single #[transition] method must return one concrete next state, so you can’t return “either Next or Other” directly. Use a small decision enum or call one of two #[transition] methods.

Example:

  #[transition]
  impl ProcessMachine<Init> {
      fn to_next(self) -> ProcessMachine<NextState> {
          self.transition()
      }

      fn to_other(self) -> ProcessMachine<OtherState> {
          self.transition()
      }
  }

  enum Decision {
      Next(ProcessMachine<NextState>),
      Other(ProcessMachine<OtherState>),
  }

  impl ProcessMachine<Init> {
      fn decide(self, event: Event) -> Decision {
          if should_go_next(event) {
              Decision::Next(self.to_next())
          } else {
              Decision::Other(self.to_other())
          }
      }
  }

So the conditional logic is supported, just not as a single #[transition]
return type.

[eboody]

i'll leave this open in case others have the same question