callbag 0.14.0

Rust implementation of the callbag spec for reactive/iterable programming
Documentation 
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use std::{
    iter::IntoIterator,
    sync::{
        atomic::{AtomicBool, Ordering as AtomicOrdering},
        Arc, RwLock,
    },
};

use crate::{Message, Source};

/// Converts an [iterable][`IntoIterator`] or [`Iterator`] to a callbag pullable source.
///
/// It only sends data when requested.
///
/// See <https://github.com/staltz/callbag-from-iter/blob/a5942d3a23da500b771d2078f296df2e41235b3a/index.js#L1-L34>
///
/// # Examples
///
/// Convert an iterable:
///
/// ```
/// use crossbeam_queue::SegQueue;
/// use std::sync::Arc;
///
/// use callbag::{for_each, from_iter};
///
/// let actual = Arc::new(SegQueue::new());
///
/// let source = from_iter([10, 20, 30, 40]);
///
/// for_each({
///     let actual = Arc::clone(&actual);
///     move |x| {
///         println!("{}", x);
///         actual.push(x);
///     }
/// })(source);
///
/// assert_eq!(
///     &{
///         let mut v = vec![];
///         for _i in 0..actual.len() {
///             v.push(actual.pop().unwrap());
///         }
///         v
///     }[..],
///     [10, 20, 30, 40]
/// );
/// ```
///
/// Convert an Iterator:
///
/// ```
/// use crossbeam_queue::SegQueue;
/// use std::sync::Arc;
///
/// use callbag::{for_each, from_iter};
///
/// let actual = Arc::new(SegQueue::new());
///
/// let source = from_iter([10, 20, 30, 40].into_iter().enumerate());
///
/// for_each({
///     let actual = Arc::clone(&actual);
///     move |x| {
///         println!("{:?}", x);
///         actual.push(x);
///     }
/// })(source);
///
/// assert_eq!(
///     &{
///         let mut v = vec![];
///         for _i in 0..actual.len() {
///             v.push(actual.pop().unwrap());
///         }
///         v
///     }[..],
///     [(0, 10), (1, 20), (2, 30), (3, 40)]
/// );
/// ```
pub fn from_iter<T: 'static, I: 'static>(iter: I) -> Source<T>
where
    T: Send + Sync,
    I: IntoIterator<Item = T> + Send + Sync + Clone,
    <I as IntoIterator>::IntoIter: Send + Sync,
{
    (move |message| {
        if let Message::Handshake(sink) = message {
            let iter = Arc::new(RwLock::new(iter.clone().into_iter()));
            let in_loop = Arc::new(AtomicBool::new(false));
            let got_pull = Arc::new(AtomicBool::new(false));
            let completed = Arc::new(AtomicBool::new(false));
            let res = Arc::new(RwLock::new(None));
            let res_done = Arc::new(AtomicBool::new(false));
            let r#loop = {
                let sink = Arc::clone(&sink);
                let in_loop = Arc::clone(&in_loop);
                let got_pull = Arc::clone(&got_pull);
                let completed = Arc::clone(&completed);
                let res_done = Arc::clone(&res_done);
                move || {
                    in_loop.store(true, AtomicOrdering::Release);
                    while got_pull.load(AtomicOrdering::Acquire)
                        && !completed.load(AtomicOrdering::Acquire)
                    {
                        got_pull.store(false, AtomicOrdering::Release);
                        {
                            let iter = &mut *iter.write().unwrap();
                            let mut res = res.write().unwrap();
                            *res = iter.next();
                            res_done.store(res.is_none(), AtomicOrdering::Release);
                        }
                        if res_done.load(AtomicOrdering::Acquire) {
                            sink(Message::Terminate);
                            break;
                        } else {
                            let res = {
                                let res = &mut *res.write().unwrap();
                                res.take().unwrap()
                            };
                            sink(Message::Data(res));
                        }
                    }
                    in_loop.store(false, AtomicOrdering::Release);
                }
            };
            sink(Message::Handshake(Arc::new(
                (move |message| {
                    if completed.load(AtomicOrdering::Acquire) {
                        return;
                    }

                    match message {
                        Message::Handshake(_) => {
                            panic!("sink handshake has already occurred");
                        },
                        Message::Data(_) => {
                            panic!("sink must not send data");
                        },
                        Message::Pull => {
                            got_pull.store(true, AtomicOrdering::Release);
                            if !in_loop.load(AtomicOrdering::Acquire)
                                && !res_done.load(AtomicOrdering::Acquire)
                            {
                                r#loop();
                            }
                        },
                        Message::Error(_) | Message::Terminate => {
                            completed.store(true, AtomicOrdering::Release);
                        },
                    }
                })
                .into(),
            )));
        }
    })
    .into()
}