auto merge of #20119 : FlaPer87/rust/oibit-send-and-friends, r=nikomatsakis

More work on opt-in built in traits. `Send` and `Sync` are not opt-in, `OwnedPtr` renamed to `UniquePtr` and the `Send` and `Sync` traits are now unsafe.

NOTE: This likely needs to be rebased on top of the yet-to-land snapshot.

r? @nikomatsakis 

cc #13231 

2 files changed, 14 insertions, 2 deletions

diff --git a/src/liballoc/arc.rs b/src/liballoc/arc.rs
index 893c9d250b7..8d8bbb42932 100644
--- a/src/liballoc/arc.rs
+++ b/src/liballoc/arc.rs
@@ -117,6 +117,10 @@ pub struct Arc<T> {
     _ptr: *mut ArcInner<T>,
 }
 
+unsafe impl<T: Sync + Send> Send for Arc<T> { }
+unsafe impl<T: Sync + Send> Sync for Arc<T> { }
+
+
 /// A weak pointer to an `Arc`.
 ///
 /// Weak pointers will not keep the data inside of the `Arc` alive, and can be used to break cycles
@@ -129,13 +133,19 @@ pub struct Weak<T> {
     _ptr: *mut ArcInner<T>,
 }
 
+unsafe impl<T: Sync + Send> Send for Weak<T> { }
+unsafe impl<T: Sync + Send> Sync for Weak<T> { }
+
 struct ArcInner<T> {
     strong: atomic::AtomicUint,
     weak: atomic::AtomicUint,
     data: T,
 }
 
-impl<T: Sync + Send> Arc<T> {
+unsafe impl<T: Sync + Send> Send for ArcInner<T> {}
+unsafe impl<T: Sync + Send> Sync for ArcInner<T> {}
+
+impl<T> Arc<T> {
     /// Constructs a new `Arc<T>`.
     ///
     /// # Examples
@@ -587,6 +597,7 @@ mod tests {
     use std::str::Str;
     use std::sync::atomic;
     use std::task;
+    use std::kinds::Send;
     use std::vec::Vec;
     use super::{Arc, Weak, weak_count, strong_count};
     use std::sync::Mutex;
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index 5fd234192c5..3c6b2d2cbc0 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -19,6 +19,7 @@ use core::hash::{mod, Hash};
 use core::kinds::Sized;
 use core::mem;
 use core::option::Option;
+use core::ptr::Unique;
 use core::raw::TraitObject;
 use core::result::Result;
 use core::result::Result::{Ok, Err};
@@ -44,7 +45,7 @@ pub static HEAP: () = ();
 /// A type that represents a uniquely-owned value.
 #[lang = "owned_box"]
 #[unstable = "custom allocators will add an additional type parameter (with default)"]
-pub struct Box<T>(*mut T);
+pub struct Box<T>(Unique<T>);
 
 #[stable]
 impl<T: Default> Default for Box<T> {