1 files changed, 81 insertions, 0 deletions
diff --git a/src/process_results_impl.rs b/src/process_results_impl.rs
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+++ b/src/process_results_impl.rs
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+
+/// An iterator that produces only the `T` values as long as the
+/// inner iterator produces `Ok(T)`.
+///
+/// Used by [`process_results`](../fn.process_results.html), see its docs
+/// for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Debug)]
+pub struct ProcessResults<'a, I, E: 'a> {
+    error: &'a mut Result<(), E>,
+    iter: I,
+}
+
+impl<'a, I, T, E> Iterator for ProcessResults<'a, I, E>
+    where I: Iterator<Item = Result<T, E>>
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.iter.next() {
+            Some(Ok(x)) => Some(x),
+            Some(Err(e)) => {
+                *self.error = Err(e);
+                None
+            }
+            None => None,
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, hi) = self.iter.size_hint();
+        (0, hi)
+    }
+}
+
+/// “Lift” a function of the values of an iterator so that it can process
+/// an iterator of `Result` values instead.
+///
+/// `iterable` is an iterator or iterable with `Result<T, E>` elements, where
+/// `T` is the value type and `E` the error type.
+///
+/// `processor` is a closure that receives an adapted version of the iterable
+/// as the only argument — the adapted iterator produces elements of type `T`,
+/// as long as the original iterator produces `Ok` values.
+///
+/// If the original iterable produces an error at any point, the adapted
+/// iterator ends and the `process_results` function will return the
+/// error iself.
+///
+/// Otherwise, the return value from the closure is returned wrapped
+/// inside `Ok`.
+///
+/// # Example
+///
+/// ```
+/// use itertools::process_results;
+///
+/// type R = Result<i32, &'static str>;
+///
+/// let first_values: Vec<R> = vec![Ok(1), Ok(0), Ok(3)];
+/// let second_values: Vec<R> = vec![Ok(2), Ok(1), Err("overflow")];
+///
+/// // “Lift” the iterator .max() method to work on the values in Results using process_results
+///
+/// let first_max = process_results(first_values, |iter| iter.max().unwrap_or(0));
+/// let second_max = process_results(second_values, |iter| iter.max().unwrap_or(0));
+///
+/// assert_eq!(first_max, Ok(3));
+/// assert!(second_max.is_err());
+/// ```
+pub fn 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>) -> R
+{
+    let iter = iterable.into_iter();
+    let mut error = Ok(());
+
+    let result = processor(ProcessResults { error: &mut error, iter });
+
+    error.map(|_| result)
+}