From 625ca7afe4fb50758215d623d45de84a5f4290ae Mon Sep 17 00:00:00 2001
From: blake2-ppc <blake2-ppc>
Date: Sat, 20 Jul 2013 19:19:13 +0200
Subject: [PATCH] option: Add .chain_mut_ref()

.chain_mut_ref() is the mutable alternative to .chain_ref().

A use case example for this method is extraction of an optional value
from an Option<Container> value.
---
 src/libstd/option.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/libstd/option.rs b/src/libstd/option.rs
index b68c67e8903b..f116c1127ca9 100644
--- a/src/libstd/option.rs
+++ b/src/libstd/option.rs
@@ -159,6 +159,17 @@ impl<T> Option<T> {
         }
     }
 
+    /// Update an optional value by optionally running its content by mut reference
+    /// through a function that returns an option.
+    #[inline]
+    pub fn chain_mut_ref<'a, U>(&'a mut self, f: &fn(x: &'a mut T) -> Option<U>)
+                                -> Option<U> {
+        match *self {
+            Some(ref mut x) => f(x),
+            None => None
+        }
+    }
+
     /// Filters an optional value using given function.
     #[inline(always)]
     pub fn filtered(self, f: &fn(t: &T) -> bool) -> Option<T> {