rx_rust/operators/combining/
switch.rs

1use crate::disposable::Disposable;
2use crate::disposable::subscription::Subscription;
3use crate::utils::types::{Mutable, MutableHelper, NecessarySendSync, Shared};
4use crate::{
5    observable::Observable,
6    observer::{Observer, Termination},
7    operators::creating::from_iter::FromIter,
8    utils::{types::MarkerType, unsub_after_termination::subscribe_unsub_after_termination},
9};
10use crate::{safe_lock_option, safe_lock_option_disposable, safe_lock_option_observer};
11use educe::Educe;
12use std::marker::PhantomData;
13
14/// Converts an Observable that emits Observables into a single Observable that emits the items emitted by the most recently emitted of those Observables.
15/// See <https://reactivex.io/documentation/operators/switch.html>
16///
17/// # Examples
18/// ```rust
19/// use rx_rust::{
20///     observable::observable_ext::ObservableExt,
21///     observer::Termination,
22///     operators::{
23///         combining::switch::Switch,
24///         creating::from_iter::FromIter,
25///     },
26/// };
27///
28/// let mut values = Vec::new();
29/// let mut terminations = Vec::new();
30///
31/// let inner_1 = FromIter::new(vec![1, 2]);
32/// let inner_2 = FromIter::new(vec![3, 4]);
33/// let observable = Switch::new_from_iter([inner_1, inner_2]);
34/// observable.subscribe_with_callback(
35///     |value| values.push(value),
36///     |termination| terminations.push(termination),
37/// );
38///
39/// assert_eq!(values, vec![1, 2, 3, 4]);
40/// assert_eq!(terminations, vec![Termination::Completed]);
41/// ```
42#[derive(Educe)]
43#[educe(Debug, Clone)]
44pub struct Switch<OE, OE1> {
45    source: OE,
46    _marker: MarkerType<OE1>,
47}
48
49impl<OE, OE1> Switch<OE, OE1> {
50    pub fn new<'or, 'sub, T, E>(source: OE) -> Self
51    where
52        OE: Observable<'or, 'sub, OE1, E>,
53        OE1: Observable<'or, 'sub, T, E>,
54    {
55        Self {
56            source,
57            _marker: PhantomData,
58        }
59    }
60}
61
62impl<OE1, I> Switch<FromIter<I>, OE1> {
63    pub fn new_from_iter<'or, 'sub, T, E>(into_iterator: I) -> Self
64    where
65        I: IntoIterator<Item = OE1>,
66        OE1: Observable<'or, 'sub, T, E>,
67    {
68        Self {
69            source: FromIter::new(into_iterator),
70            _marker: PhantomData,
71        }
72    }
73}
74
75impl<'or, 'sub, T, E, OE, OE1> Observable<'or, 'sub, T, E> for Switch<OE, OE1>
76where
77    T: 'or,
78    OE: Observable<'or, 'sub, OE1, E>,
79    OE1: Observable<'or, 'sub, T, E>,
80    'sub: 'or,
81{
82    fn subscribe(self, observer: impl Observer<T, E> + NecessarySendSync + 'or) -> Subscription<'sub> {
83        subscribe_unsub_after_termination(observer, |observer| {
84            let context = Shared::new(Mutable::new(SwitchContext {
85                on_going_sub: None,
86                completed: false,
87            }));
88            let observer = SwitchObserver {
89                observer: Shared::new(Mutable::new(Some(observer))),
90                context: context.clone(),
91                _marker: PhantomData,
92            };
93            self.source.subscribe(observer) + context
94        })
95    }
96}
97
98struct SwitchContext<'sub> {
99    on_going_sub: Option<Subscription<'sub>>,
100    completed: bool,
101}
102
103impl Disposable for Shared<Mutable<SwitchContext<'_>>> {
104    fn dispose(self) {
105        safe_lock_option_disposable!(dispose: self, on_going_sub);
106    }
107}
108
109struct SwitchObserver<'sub, T, OR> {
110    observer: Shared<Mutable<Option<OR>>>,
111    context: Shared<Mutable<SwitchContext<'sub>>>,
112    _marker: MarkerType<T>,
113}
114
115impl<'or, 'sub, T, E, OR, OE1> Observer<OE1, E> for SwitchObserver<'sub, T, OR>
116where
117    OR: Observer<T, E> + NecessarySendSync + 'or,
118    OE1: Observable<'or, 'sub, T, E>,
119    'sub: 'or,
120{
121    fn on_next(&mut self, value: OE1) {
122        // Use a placeholder subscription.
123        if let Some(on_going_sub) =
124            safe_lock_option!(replace: self.context, on_going_sub, Subscription::default())
125        {
126            on_going_sub.dispose();
127        }
128        let observer = SwitchInnerObserver {
129            observer: self.observer.clone(),
130            context: self.context.clone(),
131        };
132        let sub = value.subscribe(observer);
133        self.context.lock_mut(|mut lock| {
134            if lock.on_going_sub.is_some() {
135                lock.on_going_sub = Some(sub);
136            } else {
137                // already terminated
138            }
139        });
140    }
141
142    fn on_termination(self, termination: Termination<E>) {
143        match termination {
144            Termination::Completed => {
145                self.context.lock_mut(|mut lock| {
146                    lock.completed = true;
147                    if lock.on_going_sub.is_none() {
148                        drop(lock);
149                        safe_lock_option_observer!(on_termination: self.observer, termination);
150                    }
151                });
152            }
153            Termination::Error(_) => {
154                safe_lock_option_observer!(on_termination: self.observer, termination);
155            }
156        }
157    }
158}
159
160struct SwitchInnerObserver<'sub, OR> {
161    observer: Shared<Mutable<Option<OR>>>,
162    context: Shared<Mutable<SwitchContext<'sub>>>,
163}
164
165impl<T, E, OR> Observer<T, E> for SwitchInnerObserver<'_, OR>
166where
167    OR: Observer<T, E>,
168{
169    fn on_next(&mut self, value: T) {
170        safe_lock_option_observer!(on_next: self.observer, value);
171    }
172
173    fn on_termination(self, termination: Termination<E>) {
174        match termination {
175            Termination::Completed => {
176                self.context.lock_mut(|mut lock| {
177                    if lock.completed {
178                        drop(lock);
179                        safe_lock_option_observer!(on_termination: self.observer, termination);
180                    } else if let Some(on_going_sub) = lock.on_going_sub.take() {
181                        drop(lock);
182                        on_going_sub.dispose();
183                    }
184                });
185            }
186            Termination::Error(_) => {
187                safe_lock_option_observer!(on_termination: self.observer, termination);
188            }
189        }
190    }
191}
rx_rust/operators/combining/switch.rs

rx_rust/operators/combining/
switch.rs
