add Option::reduce

Author: Qelxiros

library/core/src/option.rs

@@ -1961,6 +1961,26 @@ impl<T> Option<T> {
             _ => None,
         }
     }
+
+    /// Reduces two options into one, using the provided function if both are `Some`.
+    ///
+    /// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some(f(s, o))`.
+    /// Otherwise, if one of `self` and `other` is `Some`, that one is returned.
+    /// Otherwise, `None` is returned.
+    #[unstable(feature = "option_reduce", issue = "144273")]
+    pub fn reduce<U, R, F>(self, other: Option<U>, f: F) -> Option<R>
+    where
+        T: Into<R>,
+        U: Into<R>,
+        F: FnOnce(T, U) -> R,
+    {
+        match (self, other) {
+            (Some(a), Some(b)) => Some(f(a, b)),
+            (Some(a), _) => Some(a.into()),
+            (_, Some(b)) => Some(b.into()),
+            _ => None,
+        }
+    }
 }
 
 impl<T, U> Option<(T, U)> {