How do I declare a Timer field in a struct?

[Maldus512]

Hello,
I'm moving to this library to manage time durations in my system. I was able to substitute my previous u32 timestamp checks and wanted to use the Timer type to articulate period tasks.

To this end I'm trying to add a Timer field to a struct that then executes a task every second. Unfortunately the Timer struct requires 4 type parameters, out of which two (State and Type) are privately owned by the timer module.
How am I supposed to declare a struct field of type Timer<Periodic, Running, Clock, Duration>?

Considering that the state of the timer (Running, Armed,...) is part of the type, I fear that mine is a use case that was not considered, as I wouldn't be able to stop or start the timer from my statically declared field. Is there no way to achieve what I want to?

[PTaylor-us]

The Timer type acts as a builder. The Timer::new() gives you a OneShot, Armed Timer object. From there, you can call Timer.into_periodic() to get a Periodic, Armed Timer object. From there you call Timer.start() to make it Running. I guess this scheme does require you to start the timer upon initialization of your struct. I can see that as being non-optimal.

my_struct.timer = Timer::new(my_clock, 1_u32.millisecond()).into_periodic().start();

If this doesn't work for your usage, let me know and I'll change it.

[Maldus512]

This is what I was trying to accomplish:

use embedded_timer::{Timer, Clock, Duration::Milliseconds};

struct MyDevice<C : Clock> {
    timer : Timer<Something, Something, C, Milliseconds<C::T>>
    /* Other stuff */
}

impl<C : Clock> MyDevice<C> {
    pub fn new(period: u32, clock : &C) -> MyDevice<C> {
        MyDevice {
            timer: Timer::new(clock, Milliseconds::new(C::T::from(period))).into_periodic(),
        }
    }

    pub fn periodic_task(&self) {
        if (self.timer.is_expired()) {
            // Do something...
            // Re-arm timer
        }
    }
}

I can get the same result (as I am currently doing) by separately storing an Instant timestamp and a Duration period to be checked, but I felt the timer route would have been more elegant. The most obvious problem is that I cannot declare the field timer of the struct, as I do not have access to the required types (where I wrote Something in my example).

Even if were able to skip that I'm afraid something would break when passing the Clock reference to the timer, unless I stored that same Clock inside the struct and made the lifetime explicit...

[PTaylor-us]

I will definitely take a close look at this and figure out what I need to change.

Even if were able to skip that I'm afraid something would break when passing the Clock reference to the timer, unless I stored that same Clock inside the struct and made the lifetime explicit...

Would you mind elaborating on this? It's entirely possible I overlooked something, but I'm not sure what issues you are concerned about. I can imagine a situation where mutable access to the Clock is needed by the implementation. Is this what you're worried about.

[Maldus512]

Would you mind elaborating on this? It's entirely possible I overlooked something, but I'm not sure what issues you are concerned about. I can imagine a situation where mutable access to the Clock is needed by the implementation. Is this what you're worried about.

Not really; truth to be told I'm still a beginner when it comes to Rust and I forgot I can indeed have multiple immutable references to an object (in this case Clock). Lifetimes and references were not clear to me in this particular context; after some more study I understood that if I want to declare a Timer field inside a struct I will just have to add an explicit lifetime parameter to account for the Clock reference inside the Timer.

[PTaylor-us]

That is good for me to know too. I too am relatively new and there are many patterns that I am not very familiar with. At the very least, I will document an example of containing a Timer in a struct. I'm guessing that perhaps you can leave one or more Timer type parameters as anonymous in the struct declaration?

[Maldus512]

I'm afraid I'm not exactly sure of what you mean by "anonymous type parameters"

[PTaylor-us]

@Maldus512 I'm updating this code. I believe making the Timer type parameters public would simplify this issue greatly. Can you confirm?

[Maldus512]

@PTaylor-us I think so. My main goal right now would be to declare a Periodic and Running timer as field/variable, and periodically check it, so exposing both type parameters as public would make it possible.

[jhbruhn]

I am struggling with the same issue. Adding the state of the timers to the type via generics is a nice idea in principle, but in prevents us from storing the timer in a struct in different states. Or am I misusing the Timer struct?
As Maldus512 said, an example on how to use the timers stored in a struct would be very nice!

Edit: On further inspection (at least for my use case), having the Timers state (Running/Armed) in the type-system is a very nice implementation in theory, but hinders me from declaring an armed Timer in a struct, which gets started in a different point in time (other than storing said timer in two Options, obviously not very elegant). Perhaps at least the Armed/Running state could be changed into an internal bool, and additionally the Markers are made public so the Timer can be defined in a struct. That would solve the problem.

[PTaylor-us]

@jhbruhn I think you're right. Given that this type may be stored in a struct, it needs to be rewritten without the state-types.

To start with, I am making the Timer param types public.

[PTaylor-us]

Related: #102