rxrust 1.0.0-rc.4

A Rust implementation of Reactive Extensions.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142

use crate::{
  context::Context,
  observable::{CoreObservable, ObservableType},
  observer::Observer,
};

#[derive(Clone)]
pub struct MapErr<S, F> {
  pub source: S,
  pub func: F,
}

pub struct MapErrObserver<O, F> {
  observer: O,
  func: F,
}

impl<O, F, Item, Err, OutErr> Observer<Item, Err> for MapErrObserver<O, F>
where
  O: Observer<Item, OutErr>,
  F: FnOnce(Err) -> OutErr,
{
  fn next(&mut self, value: Item) { self.observer.next(value); }

  fn error(self, err: Err) {
    let out_err = (self.func)(err);
    self.observer.error(out_err);
  }

  fn complete(self) { self.observer.complete(); }

  fn is_closed(&self) -> bool { self.observer.is_closed() }
}

impl<S, F, OutErr> ObservableType for MapErr<S, F>
where
  S: ObservableType,
  F: FnOnce(S::Err) -> OutErr,
{
  type Item<'a>
    = S::Item<'a>
  where
    Self: 'a;
  type Err = OutErr;
}

impl<S, F, C, OutErr> CoreObservable<C> for MapErr<S, F>
where
  C: Context,
  S: CoreObservable<C::With<MapErrObserver<C::Inner, F>>>,
  F: FnOnce(S::Err) -> OutErr,
{
  type Unsub = S::Unsub;

  fn subscribe(self, context: C) -> Self::Unsub {
    let MapErr { source, func } = self;
    let wrapped = context.transform(|observer| MapErrObserver { observer, func });
    source.subscribe(wrapped)
  }
}

#[cfg(test)]
mod tests {
  use std::{cell::RefCell, convert::Infallible, rc::Rc};

  use crate::prelude::*;

  struct AnyErrorObserver<F>(F);

  impl<F, Item, Err> Observer<Item, Err> for AnyErrorObserver<F>
  where
    F: FnMut(Item),
  {
    fn next(&mut self, value: Item) { (self.0)(value) }
    fn error(self, _err: Err) {}
    fn complete(self) {}
    fn is_closed(&self) -> bool { false }
  }

  #[rxrust_macro::test]
  fn test_map_err_transforms_error() {
    let error = Rc::new(RefCell::new(None));
    let error_clone = error.clone();

    Local::throw_err(1)
      .map_err(|e| format!("Error code: {}", e))
      .on_error(move |e| *error_clone.borrow_mut() = Some(e))
      .subscribe(|_| {});

    assert_eq!(*error.borrow(), Some("Error code: 1".to_string()));
  }

  #[rxrust_macro::test]
  fn test_map_err_passes_values() {
    let values = Rc::new(RefCell::new(Vec::new()));
    let values_clone = values.clone();
    let error = Rc::new(RefCell::new(None));
    let error_clone = error.clone();

    // o1 and o2 need to match the type of o3: Item=i32, Err=&str
    let o1 = Local::of(1)
      .map_err(|_: Infallible| "dummy")
      .box_it();
    let o2 = Local::of(2)
      .map_err(|_: Infallible| "dummy")
      .box_it();
    // o3 needs to match Item=i32
    let o3 = Local::throw_err("original error")
      .map(|_| 0)
      .box_it();

    let observables = vec![o1, o2, o3];

    // Manually create outer observable with Err=&str to match inner observables
    Local::from_iter(observables)
      .map_err(|_: Infallible| -> &str { unreachable!() })
      .concat_all()
      .map_err(|e| format!("mapped: {}", e))
      .on_error(move |e| *error_clone.borrow_mut() = Some(e))
      .subscribe_with(Local::<()>::lift(AnyErrorObserver(move |v| {
        values_clone.borrow_mut().push(v)
      })));

    assert_eq!(*values.borrow(), vec![1, 2]);
    assert_eq!(*error.borrow(), Some("mapped: original error".to_string()));
  }

  #[rxrust_macro::test]
  fn test_map_err_ignores_completion() {
    let completed = Rc::new(RefCell::new(false));
    let completed_clone = completed.clone();

    Local::of(1)
      .map_err(|_| "should not happen")
      .on_complete(move || *completed_clone.borrow_mut() = true)
      // Local::of emits Infallible error, which map_err maps to &str.
      // So we need subscribe_with because Err is not Infallible anymore.
      .subscribe_with(Local::<()>::lift(AnyErrorObserver(|_| {})));

    assert!(*completed.borrow(), "Stream should complete normally even with map_err present");
  }
}