hyphae 0.4.0

Reactive cells and runtime primitives for rship
Documentation 
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use std::sync::{
    Arc,
    atomic::{AtomicBool, Ordering},
};

use super::{CellValue, Watchable};
use crate::{
    cell::{Cell, CellImmutable, CellMutable},
    signal::Signal,
};

pub trait TakeWhileExt<T>: Watchable<T> {
    /// Take values while predicate returns true, then stop.
    #[track_caller]
    fn take_while<F>(&self, predicate: F) -> Cell<T, CellImmutable>
    where
        T: CellValue,
        F: Fn(&T) -> bool + Send + Sync + 'static,
        Self: Clone + Send + Sync + 'static,
    {
        let initial = self.get();
        let derived = Cell::<T, CellMutable>::new(initial);
        let derived = if let Some(name) = self.name() {
            derived.with_name(format!("{}::take_while", name))
        } else {
            derived
        };

        let stopped = Arc::new(AtomicBool::new(false));
        let weak = derived.downgrade();
        let first = Arc::new(AtomicBool::new(true));
        let guard = self.subscribe(move |signal| {
            if let Some(d) = weak.upgrade() {
                match signal {
                    Signal::Value(value) => {
                        if first.swap(false, Ordering::SeqCst) {
                            return;
                        }
                        if stopped.load(Ordering::SeqCst) {
                            return;
                        }
                        if !predicate(value.as_ref()) {
                            stopped.store(true, Ordering::SeqCst);
                            d.notify(Signal::Complete);
                            return;
                        }
                        d.notify(signal.clone());
                    }
                    Signal::Complete => d.notify(Signal::Complete),
                    Signal::Error(e) => d.notify(Signal::Error(e.clone())),
                }
            }
        });
        derived.own(guard);

        derived.lock()
    }
}

impl<T, W: Watchable<T>> TakeWhileExt<T> for W {}

#[cfg(test)]
mod tests {
    use std::sync::atomic::AtomicBool;

    use super::*;
    use crate::{Gettable, Mutable};

    #[test]
    fn test_take_while() {
        let source = Cell::new(1u64);
        let taken = source.take_while(|x| *x < 5);

        assert_eq!(taken.get(), 1);

        source.set(3);
        assert_eq!(taken.get(), 3);

        source.set(5); // Predicate fails, stops
        assert_eq!(taken.get(), 3);

        source.set(2); // Even though valid, already stopped
        assert_eq!(taken.get(), 3);
    }

    #[test]
    fn test_take_while_completes_on_predicate_fail() {
        let source = Cell::new(1u64);
        let taken = source.take_while(|x| *x < 5);
        let completed = Arc::new(AtomicBool::new(false));

        let c = completed.clone();
        let _guard = taken.subscribe(move |signal| {
            if let Signal::Complete = signal {
                c.store(true, Ordering::SeqCst);
            }
        });

        assert!(!taken.is_complete());

        source.set(5); // Predicate fails

        assert!(taken.is_complete());
        assert!(completed.load(Ordering::SeqCst));
    }
}