Interleave::fold

Author: Philippe-Cholet

src/adaptors/mod.rs

@@ -76,6 +76,28 @@ where
     fn size_hint(&self) -> (usize, Option<usize>) {
         size_hint::add(self.a.size_hint(), self.b.size_hint())
     }
+
+    fn fold<B, F>(self, mut init: B, mut f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        let Self { a, mut b, flag } = self;
+        if flag {
+            if let Some(y) = b.next() {
+                init = f(init, y);
+            } else {
+                return a.fold(init, f);
+            }
+        }
+        init = a.fold(init, |mut acc, x| {
+            acc = f(acc, x);
+            if let Some(y) = b.next() {
+                acc = f(acc, y);
+            }
+            acc
+        });
+        b.fold(init, f)
+    }
 }
 
 impl<I, J> FusedIterator for Interleave<I, J>