From 2cd5030ef592a2d4094145060c031dcae66e624f Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Wed, 18 Sep 2019 00:09:19 +0200
Subject: Deny specializing items not in the parent impl

---
 src/liballoc/boxed.rs | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'src/liballoc')

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index b2789a535fe..adbc0e6ba2c 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -871,6 +871,11 @@ impl<I: Iterator + ?Sized> Iterator for Box<I> {
     fn nth(&mut self, n: usize) -> Option<I::Item> {
         (**self).nth(n)
     }
+    default fn last(self) -> Option<I::Item> {
+        let mut last = None;
+        for x in self { last = Some(x); }
+        last
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-- 
cgit 1.4.1-3-g733a5


From 02f36e52a656f1baa717538e18ae96137cbc83f9 Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Wed, 18 Sep 2019 23:41:57 +0200
Subject: Hide the `Iterator` specialization behind a trait

---
 src/liballoc/boxed.rs | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

(limited to 'src/liballoc')

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index adbc0e6ba2c..9b5d9431ae2 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -871,16 +871,33 @@ impl<I: Iterator + ?Sized> Iterator for Box<I> {
     fn nth(&mut self, n: usize) -> Option<I::Item> {
         (**self).nth(n)
     }
+    fn last(self) -> Option<I::Item> {
+        BoxIter::last(self)
+    }
+}
+
+trait BoxIter {
+    type Item;
+    fn last(self) -> Option<Self::Item>;
+}
+
+impl<I: Iterator + ?Sized> BoxIter for Box<I> {
+    type Item = I::Item;
     default fn last(self) -> Option<I::Item> {
-        let mut last = None;
-        for x in self { last = Some(x); }
-        last
+        #[inline]
+        fn some<T>(_: Option<T>, x: T) -> Option<T> {
+            Some(x)
+        }
+
+        self.fold(None, some)
     }
 }
 
+/// Specialization for sized `I`s that uses `I`s implementation of `last()`
+/// instead of the default.
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<I: Iterator + Sized> Iterator for Box<I> {
-    fn last(self) -> Option<I::Item> where I: Sized {
+impl<I: Iterator> BoxIter for Box<I> {
+    fn last(self) -> Option<I::Item> {
         (*self).last()
     }
 }
-- 
cgit 1.4.1-3-g733a5