From 1135cab36576c7b8ae361a963a2294d9ea73c63c Mon Sep 17 00:00:00 2001
From: Hanif Bin Ariffin <hanif.ariffin.4326@gmail.com>
Date: Sat, 29 Aug 2020 18:56:17 -0400
Subject: [PATCH 1/3] Overload last for `Vec`.

Simply use the fact that `IntoIter` stores the end pointer and we
can perform pointer arithmetic.
---
 library/alloc/src/vec.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs
index 8526f15288fa4..6441467e3dc52 100644
--- a/library/alloc/src/vec.rs
+++ b/library/alloc/src/vec.rs
@@ -2955,6 +2955,12 @@ impl<T> Iterator for IntoIter<T> {
         unsafe {
             if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
         }
+    #[inline]
+    fn last(self) -> Option<Self::Item>
+    where
+        Self: Sized,
+    {
+        if self.ptr == self.end { None } else { unsafe { Some(ptr::read(self.end.offset(-1))) } }
     }
 }
 

From a9919e0faeaae81a5befbc819d497b3d89af8de4 Mon Sep 17 00:00:00 2001
From: Hanif Bin Ariffin <hanif.ariffin.4326@gmail.com>
Date: Sun, 30 Aug 2020 08:54:18 -0400
Subject: [PATCH 2/3] Changed the implementation of IntoIter::last()

Simply does what next() does except it goes straight to the end of the
array.

Woopsie
---
 library/alloc/src/vec.rs | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs
index 6441467e3dc52..4787c80aa494f 100644
--- a/library/alloc/src/vec.rs
+++ b/library/alloc/src/vec.rs
@@ -2956,11 +2956,23 @@ impl<T> Iterator for IntoIter<T> {
             if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
         }
     #[inline]
-    fn last(self) -> Option<Self::Item>
-    where
-        Self: Sized,
-    {
-        if self.ptr == self.end { None } else { unsafe { Some(ptr::read(self.end.offset(-1))) } }
+    fn last(mut self) -> Option<T> {
+        unsafe {
+            if self.ptr as *const _ == self.end {
+                None
+            } else {
+                if mem::size_of::<T>() == 0 {
+                    // Immediately marches to end of the iterator.
+                    self.ptr = self.end;
+                    // Make up a value of this ZST.
+                    Some(mem::zeroed())
+                } else {
+                    // Immediately marches to end of the iterator.
+                    self.ptr = self.end;
+                    Some(ptr::read(self.ptr.offset(-1)))
+                }
+            }
+        }
     }
 }
 

From 91984e7b7078c2a56d89e8e00cd8567579a508ea Mon Sep 17 00:00:00 2001
From: Hanif Bin Ariffin <hanif.ariffin.4326@gmail.com>
Date: Fri, 23 Oct 2020 14:19:59 +0800
Subject: [PATCH 3/3] Simplify the implementation of IntoIter::last() a bit.

Suggested by @pickfire.

Signed-off-by: Hanif Bin Ariffin <hanif.ariffin.4326@gmail.com>
---
 library/alloc/src/vec.rs | 19 +++----------------
 1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/library/alloc/src/vec.rs b/library/alloc/src/vec.rs
index 4787c80aa494f..4cad873190f6b 100644
--- a/library/alloc/src/vec.rs
+++ b/library/alloc/src/vec.rs
@@ -2955,24 +2955,11 @@ impl<T> Iterator for IntoIter<T> {
         unsafe {
             if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
         }
+    }
+
     #[inline]
     fn last(mut self) -> Option<T> {
-        unsafe {
-            if self.ptr as *const _ == self.end {
-                None
-            } else {
-                if mem::size_of::<T>() == 0 {
-                    // Immediately marches to end of the iterator.
-                    self.ptr = self.end;
-                    // Make up a value of this ZST.
-                    Some(mem::zeroed())
-                } else {
-                    // Immediately marches to end of the iterator.
-                    self.ptr = self.end;
-                    Some(ptr::read(self.ptr.offset(-1)))
-                }
-            }
-        }
+        self.next_back()
     }
 }