From 04b184591bb53035d2579eef8206d2e3d09cfc60 Mon Sep 17 00:00:00 2001
From: Nikolai Vazquez <nikvzqz@gmail.com>
Date: Sun, 28 Jul 2019 16:46:18 -0700
Subject: [PATCH] Add `Either::map`

---
 src/lib.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 4f81162..8a4ccbb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -581,6 +581,26 @@ impl<T> Either<T, T> {
     pub fn into_inner(self) -> T {
         either!(self, inner => inner)
     }
+
+    /// Map `f` over the contained value and return the result in the
+    /// corresponding variant.
+    ///
+    /// ```
+    /// use either::*;
+    ///
+    /// let value: Either<_, i32> = Right(42);
+    ///
+    /// let other = value.map(|x| x * 2);
+    /// assert_eq!(other, Right(84));
+    /// ```
+    pub fn map<F, M>(self, f: F) -> Either<M, M>
+        where F: FnOnce(T) -> M
+    {
+        match self {
+            Left(l) => Left(f(l)),
+            Right(r) => Right(f(r)),
+        }
+    }
 }
 
 /// Convert from `Result` to `Either` with `Ok => Right` and `Err => Left`.