1 files changed, 140 insertions, 0 deletions
diff --git a/src/iter/flatten.rs b/src/iter/flatten.rs
new file mode 100644
index 0000000..29d88f9
--- /dev/null
+++ b/src/iter/flatten.rs
@@ -0,0 +1,140 @@
+use super::plumbing::*;
+use super::*;
+
+/// `Flatten` turns each element to a parallel iterator, then flattens these iterators
+/// together. This struct is created by the [`flatten()`] method on [`ParallelIterator`].
+///
+/// [`flatten()`]: trait.ParallelIterator.html#method.flatten
+/// [`ParallelIterator`]: trait.ParallelIterator.html
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Debug, Clone)]
+pub struct Flatten<I: ParallelIterator> {
+    base: I,
+}
+
+impl<I> Flatten<I>
+where
+    I: ParallelIterator,
+    I::Item: IntoParallelIterator,
+{
+    /// Creates a new `Flatten` iterator.
+    pub(super) fn new(base: I) -> Self {
+        Flatten { base }
+    }
+}
+
+impl<I> ParallelIterator for Flatten<I>
+where
+    I: ParallelIterator,
+    I::Item: IntoParallelIterator,
+{
+    type Item = <I::Item as IntoParallelIterator>::Item;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let consumer = FlattenConsumer::new(consumer);
+        self.base.drive_unindexed(consumer)
+    }
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+/// Consumer implementation
+
+struct FlattenConsumer<C> {
+    base: C,
+}
+
+impl<C> FlattenConsumer<C> {
+    fn new(base: C) -> Self {
+        FlattenConsumer { base }
+    }
+}
+
+impl<T, C> Consumer<T> for FlattenConsumer<C>
+where
+    C: UnindexedConsumer<T::Item>,
+    T: IntoParallelIterator,
+{
+    type Folder = FlattenFolder<C, C::Result>;
+    type Reducer = C::Reducer;
+    type Result = C::Result;
+
+    fn split_at(self, index: usize) -> (Self, Self, C::Reducer) {
+        let (left, right, reducer) = self.base.split_at(index);
+        (
+            FlattenConsumer::new(left),
+            FlattenConsumer::new(right),
+            reducer,
+        )
+    }
+
+    fn into_folder(self) -> Self::Folder {
+        FlattenFolder {
+            base: self.base,
+            previous: None,
+        }
+    }
+
+    fn full(&self) -> bool {
+        self.base.full()
+    }
+}
+
+impl<T, C> UnindexedConsumer<T> for FlattenConsumer<C>
+where
+    C: UnindexedConsumer<T::Item>,
+    T: IntoParallelIterator,
+{
+    fn split_off_left(&self) -> Self {
+        FlattenConsumer::new(self.base.split_off_left())
+    }
+
+    fn to_reducer(&self) -> Self::Reducer {
+        self.base.to_reducer()
+    }
+}
+
+struct FlattenFolder<C, R> {
+    base: C,
+    previous: Option<R>,
+}
+
+impl<T, C> Folder<T> for FlattenFolder<C, C::Result>
+where
+    C: UnindexedConsumer<T::Item>,
+    T: IntoParallelIterator,
+{
+    type Result = C::Result;
+
+    fn consume(self, item: T) -> Self {
+        let par_iter = item.into_par_iter();
+        let consumer = self.base.split_off_left();
+        let result = par_iter.drive_unindexed(consumer);
+
+        let previous = match self.previous {
+            None => Some(result),
+            Some(previous) => {
+                let reducer = self.base.to_reducer();
+                Some(reducer.reduce(previous, result))
+            }
+        };
+
+        FlattenFolder {
+            base: self.base,
+            previous,
+        }
+    }
+
+    fn complete(self) -> Self::Result {
+        match self.previous {
+            Some(previous) => previous,
+            None => self.base.into_folder().complete(),
+        }
+    }
+
+    fn full(&self) -> bool {
+        self.base.full()
+    }
+}