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`](../fn.process_results.html), 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 let (_, hi) = self.iter.size_hint();
32 (0, hi)
33 }
34 }
35
36 /// “Lift” a function of the values of an iterator so that it can process
37 /// an iterator of `Result` values instead.
38 ///
39 /// `iterable` is an iterator or iterable with `Result<T, E>` elements, where
40 /// `T` is the value type and `E` the error type.
41 ///
42 /// `processor` is a closure that receives an adapted version of the iterable
43 /// as the only argument — the adapted iterator produces elements of type `T`,
44 /// as long as the original iterator produces `Ok` values.
45 ///
46 /// If the original iterable produces an error at any point, the adapted
47 /// iterator ends and the `process_results` function will return the
48 /// error iself.
49 ///
50 /// Otherwise, the return value from the closure is returned wrapped
51 /// inside `Ok`.
52 ///
53 /// # Example
54 ///
55 /// ```
56 /// use itertools::process_results;
57 ///
58 /// type R = Result<i32, &'static str>;
59 ///
60 /// let first_values: Vec<R> = vec![Ok(1), Ok(0), Ok(3)];
61 /// let second_values: Vec<R> = vec![Ok(2), Ok(1), Err("overflow")];
62 ///
63 /// // “Lift” the iterator .max() method to work on the values in Results using process_results
64 ///
65 /// let first_max = process_results(first_values, |iter| iter.max().unwrap_or(0));
66 /// let second_max = process_results(second_values, |iter| iter.max().unwrap_or(0));
67 ///
68 /// assert_eq!(first_max, Ok(3));
69 /// assert!(second_max.is_err());
70 /// ```
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>) -> R71 pub fn process_results<I, F, T, E, R>(iterable: I, processor: F) -> Result<R, E>
72 where I: IntoIterator<Item = Result<T, E>>,
73 F: FnOnce(ProcessResults<I::IntoIter, E>) -> R
74 {
75 let iter = iterable.into_iter();
76 let mut error = Ok(());
77
78 let result = processor(ProcessResults { error: &mut error, iter });
79
80 error.map(|_| result)
81 }
82