1 files changed, 147 insertions, 0 deletions
diff --git a/src/iter/flat_map_iter.rs b/src/iter/flat_map_iter.rs
new file mode 100644
index 0000000..c76cf68
--- /dev/null
+++ b/src/iter/flat_map_iter.rs
@@ -0,0 +1,147 @@
+use super::plumbing::*;
+use super::*;
+
+use std::fmt::{self, Debug};
+
+/// `FlatMapIter` maps each element to a serial iterator, then flattens these iterators together.
+/// This struct is created by the [`flat_map_iter()`] method on [`ParallelIterator`]
+///
+/// [`flat_map_iter()`]: trait.ParallelIterator.html#method.flat_map_iter
+/// [`ParallelIterator`]: trait.ParallelIterator.html
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Clone)]
+pub struct FlatMapIter<I: ParallelIterator, F> {
+    base: I,
+    map_op: F,
+}
+
+impl<I: ParallelIterator + Debug, F> Debug for FlatMapIter<I, F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("FlatMapIter")
+            .field("base", &self.base)
+            .finish()
+    }
+}
+
+impl<I: ParallelIterator, F> FlatMapIter<I, F> {
+    /// Creates a new `FlatMapIter` iterator.
+    pub(super) fn new(base: I, map_op: F) -> Self {
+        FlatMapIter { base, map_op }
+    }
+}
+
+impl<I, F, SI> ParallelIterator for FlatMapIter<I, F>
+where
+    I: ParallelIterator,
+    F: Fn(I::Item) -> SI + Sync + Send,
+    SI: IntoIterator,
+    SI::Item: Send,
+{
+    type Item = SI::Item;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let consumer = FlatMapIterConsumer::new(consumer, &self.map_op);
+        self.base.drive_unindexed(consumer)
+    }
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+/// Consumer implementation
+
+struct FlatMapIterConsumer<'f, C, F> {
+    base: C,
+    map_op: &'f F,
+}
+
+impl<'f, C, F> FlatMapIterConsumer<'f, C, F> {
+    fn new(base: C, map_op: &'f F) -> Self {
+        FlatMapIterConsumer { base, map_op }
+    }
+}
+
+impl<'f, T, U, C, F> Consumer<T> for FlatMapIterConsumer<'f, C, F>
+where
+    C: UnindexedConsumer<U::Item>,
+    F: Fn(T) -> U + Sync,
+    U: IntoIterator,
+{
+    type Folder = FlatMapIterFolder<'f, C::Folder, F>;
+    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);
+        (
+            FlatMapIterConsumer::new(left, self.map_op),
+            FlatMapIterConsumer::new(right, self.map_op),
+            reducer,
+        )
+    }
+
+    fn into_folder(self) -> Self::Folder {
+        FlatMapIterFolder {
+            base: self.base.into_folder(),
+            map_op: self.map_op,
+        }
+    }
+
+    fn full(&self) -> bool {
+        self.base.full()
+    }
+}
+
+impl<'f, T, U, C, F> UnindexedConsumer<T> for FlatMapIterConsumer<'f, C, F>
+where
+    C: UnindexedConsumer<U::Item>,
+    F: Fn(T) -> U + Sync,
+    U: IntoIterator,
+{
+    fn split_off_left(&self) -> Self {
+        FlatMapIterConsumer::new(self.base.split_off_left(), self.map_op)
+    }
+
+    fn to_reducer(&self) -> Self::Reducer {
+        self.base.to_reducer()
+    }
+}
+
+struct FlatMapIterFolder<'f, C, F> {
+    base: C,
+    map_op: &'f F,
+}
+
+impl<'f, T, U, C, F> Folder<T> for FlatMapIterFolder<'f, C, F>
+where
+    C: Folder<U::Item>,
+    F: Fn(T) -> U,
+    U: IntoIterator,
+{
+    type Result = C::Result;
+
+    fn consume(self, item: T) -> Self {
+        let map_op = self.map_op;
+        let base = self.base.consume_iter(map_op(item));
+        FlatMapIterFolder { base, map_op }
+    }
+
+    fn consume_iter<I>(self, iter: I) -> Self
+    where
+        I: IntoIterator<Item = T>,
+    {
+        let map_op = self.map_op;
+        let iter = iter.into_iter().flat_map(map_op);
+        let base = self.base.consume_iter(iter);
+        FlatMapIterFolder { base, map_op }
+    }
+
+    fn complete(self) -> Self::Result {
+        self.base.complete()
+    }
+
+    fn full(&self) -> bool {
+        self.base.full()
+    }
+}