Rewrite Unique<T> so that it is covariant in T, implies NonZero and ownership,

and also follows the API of `NonZero` a bit more closely. More to do
here I think (including perhaps a new name).

Author: nikomatsakis

src/libcore/nonzero.rs

@@ -10,15 +10,14 @@
 
 //! Exposes the NonZero lang item which provides optimization hints.
 
+use marker::{Sized, MarkerTrait};
 use ops::Deref;
-use ptr::Unique;
 
 /// Unsafe trait to indicate what types are usable with the NonZero struct
-pub unsafe trait Zeroable {}
+pub unsafe trait Zeroable : MarkerTrait {}
 
-unsafe impl<T> Zeroable for *const T {}
-unsafe impl<T> Zeroable for *mut T {}
-unsafe impl<T> Zeroable for Unique<T> { }
+unsafe impl<T:?Sized> Zeroable for *const T {}
+unsafe impl<T:?Sized> Zeroable for *mut T {}
 unsafe impl Zeroable for isize {}
 unsafe impl Zeroable for usize {}
 unsafe impl Zeroable for i8 {}

src/libcore/ptr.rs

@@ -91,8 +91,10 @@
 use mem;
 use clone::Clone;
 use intrinsics;
+use ops::Deref;
 use option::Option::{self, Some, None};
-use marker::{self, Send, Sized, Sync};
+use marker::{PhantomData, Send, Sized, Sync};
+use nonzero::NonZero;
 
 use cmp::{PartialEq, Eq, Ord, PartialOrd};
 use cmp::Ordering::{self, Less, Equal, Greater};
@@ -517,15 +519,16 @@ impl<T> PartialOrd for *mut T {
 
 /// A wrapper around a raw `*mut T` that indicates that the possessor
 /// of this wrapper owns the referent. This in turn implies that the
-/// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a
-/// raw `*mut T` (which conveys no particular ownership semantics).
-/// Useful for building abstractions like `Vec<T>` or `Box<T>`, which
+/// `Unique<T>` is `Send`/`Sync` if `T` is `Send`/`Sync`, unlike a raw
+/// `*mut T` (which conveys no particular ownership semantics).  It
+/// also implies that the referent of the pointer should not be
+/// modified without a unique path to the `Unique` reference. Useful
+/// for building abstractions like `Vec<T>` or `Box<T>`, which
 /// internally use raw pointers to manage the memory that they own.
 #[unstable(feature = "core", reason = "recently added to this module")]
-pub struct Unique<T: ?Sized> {
-    /// The wrapped `*mut T`.
-    pub ptr: *mut T,
-    _own: marker::PhantomData<T>,
+pub struct Unique<T:?Sized> {
+    pointer: NonZero<*const T>,
+    _marker: PhantomData<T>,
 }
 
 /// `Unique` pointers are `Send` if `T` is `Send` because the data they
@@ -542,25 +545,34 @@ unsafe impl<T: Send + ?Sized> Send for Unique<T> { }
 #[unstable(feature = "core", reason = "recently added to this module")]
 unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }
 
-impl<T> Unique<T> {
-    /// Returns a null Unique.
+impl<T:?Sized> Unique<T> {
+    /// Create a new `Unique`.
     #[unstable(feature = "core",
                reason = "recently added to this module")]
-    pub fn null() -> Unique<T> {
-        Unique(null_mut())
+    pub unsafe fn new(ptr: *mut T) -> Unique<T> {
+        Unique { pointer: NonZero::new(ptr as *const T), _marker: PhantomData }
     }
 
-    /// Return an (unsafe) pointer into the memory owned by `self`.
+    /// Dereference the content.
     #[unstable(feature = "core",
                reason = "recently added to this module")]
-    pub unsafe fn offset(self, offset: isize) -> *mut T {
-        self.ptr.offset(offset)
+    pub unsafe fn get(&self) -> &T {
+        &**self.pointer
+    }
+
+    /// Mutably dereference the content.
+    #[unstable(feature = "core",
+               reason = "recently added to this module")]
+    pub unsafe fn get_mut(&mut self) -> &mut T {
+        &mut ***self
     }
 }
 
-/// Creates a `Unique` wrapped around `ptr`, taking ownership of the
-/// data referenced by `ptr`.
-#[allow(non_snake_case)]
-pub fn Unique<T: ?Sized>(ptr: *mut T) -> Unique<T> {
-    Unique { ptr: ptr, _own: marker::PhantomData }
+impl<T:?Sized> Deref for Unique<T> {
+    type Target = *mut T;
+
+    #[inline]
+    fn deref<'a>(&'a self) -> &'a *mut T {
+        unsafe { mem::transmute(&*self.pointer) }
+    }
 }

src/libcoretest/ptr.rs

@@ -171,8 +171,8 @@ fn test_set_memory() {
 #[test]
 fn test_unsized_unique() {
     let xs: &mut [_] = &mut [1, 2, 3];
-    let ptr = Unique(xs as *mut [_]);
-    let ys = unsafe { &mut *ptr.ptr };
+    let ptr = unsafe { Unique::new(xs as *mut [_]) };
+    let ys = unsafe { &mut **ptr };
     let zs: &mut [_] = &mut [1, 2, 3];
     assert!(ys == zs);
 }