UniqueBy::next_back: use rfind

Author: Philippe-Cholet

src/unique_impl.rs

@@ -84,13 +84,8 @@ where
     F: FnMut(&I::Item) -> V,
 {
     fn next_back(&mut self) -> Option<Self::Item> {
-        while let Some(v) = self.iter.next_back() {
-            let key = (self.f)(&v);
-            if self.used.insert(key, ()).is_none() {
-                return Some(v);
-            }
-        }
-        None
+        let Self { iter, used, f } = self;
+        iter.rfind(|v| used.insert(f(v), ()).is_none())
     }
 }