make Result::map_or_else consistent with Option::map_or_else

src/libcore/result.rs

@@ -540,8 +540,11 @@ impl<T, E> Result<T, E> {
     /// ```
     #[inline]
     #[unstable(feature = "result_map_or_else", issue = "53268")]
-    pub fn map_or_else<U, M: FnOnce(T) -> U, F: FnOnce(E) -> U>(self, fallback: F, map: M) -> U {
-        self.map(map).unwrap_or_else(fallback)
+    pub fn map_or_else<U, D: FnOnce(E) -> U, F: FnOnce(T) -> U>(self, default: D, f: F) -> U {
+        match self {
+            Ok(t) => f(t),
+            Err(e) => default(e),
+        }
     }
 
     /// Maps a `Result<T, E>` to `Result<T, F>` by applying a function to a