1
2 /// An iterator that produces only the `T` values as long as the
3 /// inner iterator produces `Ok(T)`.
4 ///
5 /// Used by [`process_results`](crate::process_results), see its docs
6 /// for more information.
7 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
8 #[derive(Debug)]
9 pub struct ProcessResults<'a, I, E: 'a> {
10 error: &'a mut Result<(), E>,
11 iter: I,
12 }
13
14 impl<'a, I, T, E> Iterator for ProcessResults<'a, I, E>
15 where I: Iterator<Item = Result<T, E>>
16 {
17 type Item = T;
18
next(&mut self) -> Option<Self::Item>19 fn next(&mut self) -> Option<Self::Item> {
20 match self.iter.next() {
21 Some(Ok(x)) => Some(x),
22 Some(Err(e)) => {
23 *self.error = Err(e);
24 None
25 }
26 None => None,
27 }
28 }
29
size_hint(&self) -> (usize, Option<usize>)30 fn size_hint(&self) -> (usize, Option<usize>) {
31 (0, self.iter.size_hint().1)
32 }
33 }
34
35 /// “Lift” a function of the values of an iterator so that it can process
36 /// an iterator of `Result` values instead.
37 ///
38 /// `iterable` is an iterator or iterable with `Result<T, E>` elements, where
39 /// `T` is the value type and `E` the error type.
40 ///
41 /// `processor` is a closure that receives an adapted version of the iterable
42 /// as the only argument — the adapted iterator produces elements of type `T`,
43 /// as long as the original iterator produces `Ok` values.
44 ///
45 /// If the original iterable produces an error at any point, the adapted
46 /// iterator ends and the `process_results` function will return the
47 /// error iself.
48 ///
49 /// Otherwise, the return value from the closure is returned wrapped
50 /// inside `Ok`.
51 ///
52 /// # Example
53 ///
54 /// ```
55 /// use itertools::process_results;
56 ///
57 /// type R = Result<i32, &'static str>;
58 ///
59 /// let first_values: Vec<R> = vec![Ok(1), Ok(0), Ok(3)];
60 /// let second_values: Vec<R> = vec![Ok(2), Ok(1), Err("overflow")];
61 ///
62 /// // “Lift” the iterator .max() method to work on the values in Results using process_results
63 ///
64 /// let first_max = process_results(first_values, |iter| iter.max().unwrap_or(0));
65 /// let second_max = process_results(second_values, |iter| iter.max().unwrap_or(0));
66 ///
67 /// assert_eq!(first_max, Ok(3));
68 /// assert!(second_max.is_err());
69 /// ```
process_results<I, F, T, E, R>(iterable: I, processor: F) -> Result<R, E> where I: IntoIterator<Item = Result<T, E>>, F: FnOnce(ProcessResults<I::IntoIter, E>) -> R70 pub fn process_results<I, F, T, E, R>(iterable: I, processor: F) -> Result<R, E>
71 where I: IntoIterator<Item = Result<T, E>>,
72 F: FnOnce(ProcessResults<I::IntoIter, E>) -> R
73 {
74 let iter = iterable.into_iter();
75 let mut error = Ok(());
76
77 let result = processor(ProcessResults { error: &mut error, iter });
78
79 error.map(|_| result)
80 }
81