Add find_or_last method to Itertools trait

src/lib.rs

@@ -1730,7 +1730,31 @@ pub trait Itertools : Iterator {
         }
         None
     }
+    /// Find the value of the first element satisfying a predicate or return the last element, if any.
+    ///
+    /// The iterator is not advanced past the first element found.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let numbers = [1, 2, 3, 4];
+    /// assert_eq!(numbers.iter().find_or_last(|&&x| x > 5), Some(&4));
+    /// assert_eq!(numbers.iter().find_or_last(|&&x| x > 2), Some(&3));
+    /// assert_eq!(std::iter::empty::<i32>().find_or_last(|&x| x > 5), None);
+    /// ```
+    fn find_or_last<P>(mut self, predicate: P) -> Option<Self::Item>
+        where Self: Sized,
+              P: FnMut(&Self::Item) -> bool,
+    {
+        #[inline]
+        fn check<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut(Option<T>, T) -> Result<Option<T>, T> {
+            move |_, x| {
+                if predicate(&x) { Result::Err(x) } else { Result::Ok(Some(x)) }
+            }
+        }
 
+        self.try_fold(None, check(predicate)).unwrap_or_else(Some)
+    }
     /// Returns `true` if the given item is present in this iterator.
     ///
     /// This method is short-circuiting. If the given item is present in this