98 lines
2.9 KiB
Rust
98 lines
2.9 KiB
Rust
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/// An iterator that produces only the `T` values as long as the
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/// inner iterator produces `Ok(T)`.
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///
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/// Used by [`process_results`](crate::process_results), see its docs
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/// for more information.
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#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
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#[derive(Debug)]
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pub struct ProcessResults<'a, I, E: 'a> {
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error: &'a mut Result<(), E>,
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iter: I,
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}
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impl<'a, I, T, E> Iterator for ProcessResults<'a, I, E>
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where I: Iterator<Item = Result<T, E>>
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{
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type Item = T;
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fn next(&mut self) -> Option<Self::Item> {
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match self.iter.next() {
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Some(Ok(x)) => Some(x),
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Some(Err(e)) => {
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*self.error = Err(e);
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None
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}
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None => None,
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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(0, self.iter.size_hint().1)
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}
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fn fold<B, F>(mut self, init: B, mut f: F) -> B
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where
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Self: Sized,
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F: FnMut(B, Self::Item) -> B,
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{
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let error = self.error;
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self.iter
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.try_fold(init, |acc, opt| match opt {
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Ok(x) => Ok(f(acc, x)),
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Err(e) => {
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*error = Err(e);
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Err(acc)
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}
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})
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.unwrap_or_else(|e| e)
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}
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}
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/// “Lift” a function of the values of an iterator so that it can process
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/// an iterator of `Result` values instead.
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///
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/// `iterable` is an iterator or iterable with `Result<T, E>` elements, where
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/// `T` is the value type and `E` the error type.
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///
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/// `processor` is a closure that receives an adapted version of the iterable
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/// as the only argument — the adapted iterator produces elements of type `T`,
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/// as long as the original iterator produces `Ok` values.
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///
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/// If the original iterable produces an error at any point, the adapted
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/// iterator ends and the `process_results` function will return the
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/// error iself.
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///
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/// Otherwise, the return value from the closure is returned wrapped
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/// inside `Ok`.
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///
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/// # Example
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///
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/// ```
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/// use itertools::process_results;
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///
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/// type R = Result<i32, &'static str>;
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///
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/// let first_values: Vec<R> = vec![Ok(1), Ok(0), Ok(3)];
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/// let second_values: Vec<R> = vec![Ok(2), Ok(1), Err("overflow")];
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///
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/// // “Lift” the iterator .max() method to work on the values in Results using process_results
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///
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/// let first_max = process_results(first_values, |iter| iter.max().unwrap_or(0));
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/// let second_max = process_results(second_values, |iter| iter.max().unwrap_or(0));
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///
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/// assert_eq!(first_max, Ok(3));
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/// assert!(second_max.is_err());
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/// ```
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pub fn process_results<I, F, T, E, R>(iterable: I, processor: F) -> Result<R, E>
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where I: IntoIterator<Item = Result<T, E>>,
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F: FnOnce(ProcessResults<I::IntoIter, E>) -> R
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{
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let iter = iterable.into_iter();
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let mut error = Ok(());
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let result = processor(ProcessResults { error: &mut error, iter });
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error.map(|_| result)
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}
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