rx_rust/operators/utility/
do_before_next.rs

1use crate::utils::types::MaybeSend;
2use crate::{
3    observable::Observable,
4    observable::Subscription,
5    observer::{Flow, Observer},
6};
7use educe::Educe;
8
9/// Invokes a callback for each item emitted by the source Observable before the item is emitted to the downstream observer.
10/// See <https://reactivex.io/documentation/operators/do.html>
11///
12/// # Examples
13/// ```rust
14/// use rx_rust::{
15///     observable::ObservableExt,
16///     observer::Termination,
17///     operators::{
18///         creating::from_iter::FromIter,
19///         utility::do_before_next::DoBeforeNext,
20///     },
21/// };
22/// use std::sync::{Arc, Mutex};
23///
24/// let mut values = Vec::new();
25/// let mut terminations = Vec::new();
26/// let side_effects = Arc::new(Mutex::new(Vec::new()));
27/// let side_effects_observer = Arc::clone(&side_effects);
28///
29/// DoBeforeNext::new(FromIter::new(vec![1, 2]), move |value: &i32| {
30///     side_effects_observer.lock().unwrap().push(*value * 10);
31/// })
32/// .subscribe_with_callback(
33///     |value| values.push(value),
34///     |termination| terminations.push(termination),
35/// );
36///
37/// assert_eq!(values, vec![1, 2]);
38/// assert_eq!(terminations, vec![Termination::Completed]);
39/// assert_eq!(&*side_effects.lock().unwrap(), &[10, 20]);
40/// ```
41#[derive(Educe)]
42#[educe(Debug, Clone)]
43pub struct DoBeforeNext<OE, F> {
44    source: OE,
45    callback: F,
46}
47
48impl<OE, F> DoBeforeNext<OE, F> {
49    pub fn new<'or, T, E>(source: OE, callback: F) -> Self
50    where
51        OE: Observable<'or, T, E>,
52        F: FnMut(&T),
53    {
54        Self { source, callback }
55    }
56}
57
58impl<'or, T, E, OE, F> Observable<'or, T, E> for DoBeforeNext<OE, F>
59where
60    OE: Observable<'or, T, E>,
61    F: FnMut(&T) + MaybeSend + 'or,
62{
63    type D = OE::D;
64
65    fn subscribe(self, observer: impl Observer<T, E> + MaybeSend + 'or) -> Subscription<Self::D> {
66        self.source.subscribe(DoBeforeNextObserver {
67            observer,
68            callback: self.callback,
69        })
70    }
71}
72
73struct DoBeforeNextObserver<OR, F> {
74    observer: OR,
75    callback: F,
76}
77
78impl<T, E, OR, F> Observer<T, E> for DoBeforeNextObserver<OR, F>
79where
80    OR: Observer<T, E>,
81    F: FnMut(&T),
82{
83    fn on_next(&mut self, value: T) -> Flow {
84        (self.callback)(&value);
85        self.observer.on_next(value)
86    }
87
88    fn on_termination(self, termination: crate::observer::Termination<E>) {
89        self.observer.on_termination(termination);
90    }
91}
rx_rust/operators/utility/do_before_next.rs

rx_rust/operators/utility/
do_before_next.rs
