1 files changed, 116 insertions, 0 deletions
diff --git a/src/iter/reduce.rs b/src/iter/reduce.rs
new file mode 100644
index 0000000..321b5dd
--- /dev/null
+++ b/src/iter/reduce.rs
@@ -0,0 +1,116 @@
+use super::plumbing::*;
+use super::ParallelIterator;
+
+pub(super) fn reduce<PI, R, ID, T>(pi: PI, identity: ID, reduce_op: R) -> T
+where
+    PI: ParallelIterator<Item = T>,
+    R: Fn(T, T) -> T + Sync,
+    ID: Fn() -> T + Sync,
+    T: Send,
+{
+    let consumer = ReduceConsumer {
+        identity: &identity,
+        reduce_op: &reduce_op,
+    };
+    pi.drive_unindexed(consumer)
+}
+
+struct ReduceConsumer<'r, R, ID> {
+    identity: &'r ID,
+    reduce_op: &'r R,
+}
+
+impl<'r, R, ID> Copy for ReduceConsumer<'r, R, ID> {}
+
+impl<'r, R, ID> Clone for ReduceConsumer<'r, R, ID> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<'r, R, ID, T> Consumer<T> for ReduceConsumer<'r, R, ID>
+where
+    R: Fn(T, T) -> T + Sync,
+    ID: Fn() -> T + Sync,
+    T: Send,
+{
+    type Folder = ReduceFolder<'r, R, T>;
+    type Reducer = Self;
+    type Result = T;
+
+    fn split_at(self, _index: usize) -> (Self, Self, Self) {
+        (self, self, self)
+    }
+
+    fn into_folder(self) -> Self::Folder {
+        ReduceFolder {
+            reduce_op: self.reduce_op,
+            item: (self.identity)(),
+        }
+    }
+
+    fn full(&self) -> bool {
+        false
+    }
+}
+
+impl<'r, R, ID, T> UnindexedConsumer<T> for ReduceConsumer<'r, R, ID>
+where
+    R: Fn(T, T) -> T + Sync,
+    ID: Fn() -> T + Sync,
+    T: Send,
+{
+    fn split_off_left(&self) -> Self {
+        *self
+    }
+
+    fn to_reducer(&self) -> Self::Reducer {
+        *self
+    }
+}
+
+impl<'r, R, ID, T> Reducer<T> for ReduceConsumer<'r, R, ID>
+where
+    R: Fn(T, T) -> T + Sync,
+{
+    fn reduce(self, left: T, right: T) -> T {
+        (self.reduce_op)(left, right)
+    }
+}
+
+struct ReduceFolder<'r, R, T> {
+    reduce_op: &'r R,
+    item: T,
+}
+
+impl<'r, R, T> Folder<T> for ReduceFolder<'r, R, T>
+where
+    R: Fn(T, T) -> T,
+{
+    type Result = T;
+
+    fn consume(self, item: T) -> Self {
+        ReduceFolder {
+            reduce_op: self.reduce_op,
+            item: (self.reduce_op)(self.item, item),
+        }
+    }
+
+    fn consume_iter<I>(self, iter: I) -> Self
+    where
+        I: IntoIterator<Item = T>,
+    {
+        ReduceFolder {
+            reduce_op: self.reduce_op,
+            item: iter.into_iter().fold(self.item, self.reduce_op),
+        }
+    }
+
+    fn complete(self) -> T {
+        self.item
+    }
+
+    fn full(&self) -> bool {
+        false
+    }
+}