Pass reference values in guards and owned values in actions

[oblique]

Closes #48

[oblique]

Let me know if you have any comments

[ryan-summers]

The changes seem reasonable to me. This will definitely have some impact on fallible actions support though discussed in #44, but I don't think that should block a change like this. There's definitely value in simply moving data instead of using references and letting the compiler be smart about copying/cloning as appropriate.

[oblique]

Pushed new changes. I avoided panicking, however fn state still needs unwrap, so I used unwrap_unchecked instead, but I don't like that it is unsafe.

If you have any other ideas let me know.

[oblique]

I had an idea today to introduce Error::Poisoned. Normally this error should never happen, but it's the only way to avoid unwrap without unsafe.

These are the reasons that this error will happen:

• smlang did not restore the self.state to Some. For example before returning GuardFailed or InvalidEvent.
• The user panicked in guard or action functions, so the self.state was not restored to Some.

This is the generated code:

    #[inline(always)]
    pub fn state(&self) -> Result<&States, Error> {
        self.state.as_ref().ok_or_else(|| Error::Poisoned)
    }

    pub fn process_event(&mut self, mut event: Events) -> Result<&States, Error> {
        match self.state.take().ok_or_else(|| Error::Poisoned)? {
            States::State1 => match event {
                Events::Event1(event_data) => {
                    match self.context.guard1(&event_data) {
                        Ok(()) => {
                            let _data = self.context.action1(event_data);
                            self.state = Some(States::State2(_data));
                        }
                        Err(e) => {
                            self.state = Some(States::State1);
                            return Err(Error::GuardFailed(e));
                        }
                    }
                    self.state()
                }
                _ => {
                    self.state = Some(States::State1);
                    Err(Error::InvalidEvent)
                }
            },
            States::State2(state_data) => match event {
                _ => {
                    self.state = Some(States::State2(state_data));
                    Err(Error::InvalidEvent)
                }
            },
            state => {
                self.state = Some(state);
                Err(Error::InvalidEvent)
            }
        }
    }

[oblique]

Rebased. Now the generated code is:

    pub fn state(&self) -> Result<&States, Error> {
        self.state.as_ref().ok_or_else(|| Error::Poisoned)
    }

    pub fn process_event(&mut self, mut event: Events) -> Result<&States, Error> {
        match self.state.take().ok_or_else(|| Error::Poisoned)? {
            States::State1 => match event {
                Events::Event1(event_data) => {
                    if let Err(e) = self.context.guard1(&event_data) {
                        self.state = Some(States::State1);
                        return Err(Error::GuardFailed(e));
                    }
                    let _data = self.context.action1(event_data);
                    self.state = Some(States::State2(_data));
                    self.state()
                }
                _ => {
                    self.state = Some(States::State1);
                    Err(Error::InvalidEvent)
                }
            },
            States::State2(state_data) => match event {
                _ => {
                    self.state = Some(States::State2(state_data));
                    Err(Error::InvalidEvent)
                }
            },
            state => {
                self.state = Some(state);
                Err(Error::InvalidEvent)
            }
        }
    }

[ryan-summers]

I'd like to let this kind of change rest for a bit before releasing it. There's some implications of moving state data that I'm not sure I've fully understood yet.

[ryan-summers]

LGTM. Thanks for persisting through my nagging :)