From d882491158a29f58131c86d12272b350037b78c1 Mon Sep 17 00:00:00 2001
From: Xenira <1288524+Xenira@users.noreply.github.com>
Date: Mon, 27 May 2024 20:00:38 +0200
Subject: [PATCH] feat(`FilterOk`): implement `DoubleEndedIterator`

Refs: #947
---
 benches/specializations.rs |  1 +
 src/adaptors/mod.rs        | 24 ++++++++++++++++++++++++
 tests/specializations.rs   |  4 +++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/benches/specializations.rs b/benches/specializations.rs
index 18039fc4e..958bcc124 100644
--- a/benches/specializations.rs
+++ b/benches/specializations.rs
@@ -639,6 +639,7 @@ bench_specializations! {
         v.iter().copied().map_ok(|x| x + 1)
     }
     filter_ok {
+        DoubleEndedIterator
         {
             let v = black_box((0_u32..1024)
                 .map(|x| if x % 2 == 1 { Err(x) } else { Ok(x) })
diff --git a/src/adaptors/mod.rs b/src/adaptors/mod.rs
index 6f5e0260e..e757837b7 100644
--- a/src/adaptors/mod.rs
+++ b/src/adaptors/mod.rs
@@ -936,6 +936,30 @@ where
     }
 }
 
+impl<I, F, T, E> DoubleEndedIterator for FilterOk<I, F>
+where
+    I: DoubleEndedIterator<Item = Result<T, E>>,
+    F: FnMut(&T) -> bool,
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        let f = &mut self.f;
+        self.iter.rfind(|res| match res {
+            Ok(t) => f(t),
+            _ => true,
+        })
+    }
+
+    fn rfold<Acc, Fold>(self, init: Acc, fold_f: Fold) -> Acc
+    where
+        Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter
+            .filter(|v| v.as_ref().map(&mut f).unwrap_or(true))
+            .rfold(init, fold_f)
+    }
+}
+
 impl<I, F, T, E> FusedIterator for FilterOk<I, F>
 where
     I: FusedIterator<Item = Result<T, E>>,
diff --git a/tests/specializations.rs b/tests/specializations.rs
index 712311472..cdc51fb23 100644
--- a/tests/specializations.rs
+++ b/tests/specializations.rs
@@ -447,7 +447,9 @@ quickcheck! {
     }
 
     fn filter_ok(v: Vec<Result<u8, char>>) -> () {
-        test_specializations(&v.into_iter().filter_ok(|&i| i < 20));
+        let it = v.into_iter().filter_ok(|&i| i < 20);
+        test_specializations(&it);
+        test_double_ended_specializations(&it);
     }
 
     fn filter_map_ok(v: Vec<Result<u8, char>>) -> () {