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    // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    // FIXME: talk about offset, copy_memory, copy_nonoverlapping_memory

    //! Raw, unsafe pointers, `*const T`, and `*mut T`.
    //!
    //! *[See also the pointer primitive types](../../std/primitive.pointer.html).*

    #![stable(feature = "rust1", since = "1.0.0")]

    use clone::Clone;
    use intrinsics;
    use ops::{CoerceUnsized, Deref};
    use fmt;
    use hash;
    use option::Option::{self, Some, None};
    use marker::{Copy, PhantomData, Send, Sized, Sync, Unsize};
    use mem;
    use nonzero::NonZero;

    use cmp::{PartialEq, Eq, Ord, PartialOrd};
    use cmp::Ordering::{self, Less, Equal, Greater};

    // FIXME #19649: intrinsic docs don't render, so these have no docs :(

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use intrinsics::copy_nonoverlapping;

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use intrinsics::copy;

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use intrinsics::write_bytes;

    #[stable(feature = "drop_in_place", since = "1.8.0")]
    pub use intrinsics::drop_in_place;

    /// Creates a null raw pointer.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ptr;
    ///
    /// let p: *const i32 = ptr::null();
    /// assert!(p.is_null());
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub const fn null<T>() -> *const T { 0 as *const T }

    /// Creates a null mutable raw pointer.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ptr;
    ///
    /// let p: *mut i32 = ptr::null_mut();
    /// assert!(p.is_null());
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub const fn null_mut<T>() -> *mut T { 0 as *mut T }

    /// Swaps the values at two mutable locations of the same type, without
    /// deinitializing either. They may overlap, unlike `mem::swap` which is
    /// otherwise equivalent.
    ///
    /// # Safety
    ///
    /// This is only unsafe because it accepts a raw pointer.
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn swap<T>(x: *mut T, y: *mut T) {
        // Give ourselves some scratch space to work with
        let mut tmp: T = mem::uninitialized();

        // Perform the swap
        copy_nonoverlapping(x, &mut tmp, 1);
        copy(y, x, 1); // `x` and `y` may overlap
        copy_nonoverlapping(&tmp, y, 1);

        // y and t now point to the same thing, but we need to completely forget `tmp`
        // because it's no longer relevant.
        mem::forget(tmp);
    }

    /// Replaces the value at `dest` with `src`, returning the old
    /// value, without dropping either.
    ///
    /// # Safety
    ///
    /// This is only unsafe because it accepts a raw pointer.
    /// Otherwise, this operation is identical to `mem::replace`.
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn replace<T>(dest: *mut T, mut src: T) -> T {
        mem::swap(&mut *dest, &mut src); // cannot overlap
        src
    }

    /// Reads the value from `src` without moving it. This leaves the
    /// memory in `src` unchanged.
    ///
    /// # Safety
    ///
    /// Beyond accepting a raw pointer, this is unsafe because it semantically
    /// moves the value out of `src` without preventing further usage of `src`.
    /// If `T` is not `Copy`, then care must be taken to ensure that the value at
    /// `src` is not used before the data is overwritten again (e.g. with `write`,
    /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
    /// because it will attempt to drop the value previously at `*src`.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let x = 12;
    /// let y = &x as *const i32;
    ///
    /// unsafe { println!("{}", std::ptr::read(y)); }
    /// ```
    #[inline(always)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn read<T>(src: *const T) -> T {
        let mut tmp: T = mem::uninitialized();
        copy_nonoverlapping(src, &mut tmp, 1);
        tmp
    }

    #[allow(missing_docs)]
    #[inline(always)]
    #[unstable(feature = "filling_drop",
               reason = "may play a larger role in std::ptr future extensions",
               issue = "5016")]
    pub unsafe fn read_and_drop<T>(dest: *mut T) -> T {
        // Copy the data out from `dest`:
        let tmp = read(&*dest);

        // Now mark `dest` as dropped:
        write_bytes(dest, mem::POST_DROP_U8, 1);

        tmp
    }

    /// Overwrites a memory location with the given value without reading or
    /// dropping the old value.
    ///
    /// # Safety
    ///
    /// This operation is marked unsafe because it accepts a raw pointer.
    ///
    /// It does not drop the contents of `dst`. This is safe, but it could leak
    /// allocations or resources, so care must be taken not to overwrite an object
    /// that should be dropped.
    ///
    /// This is appropriate for initializing uninitialized memory, or overwriting
    /// memory that has previously been `read` from.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let mut x = 0;
    /// let y = &mut x as *mut i32;
    /// let z = 12;
    ///
    /// unsafe {
    ///     std::ptr::write(y, z);
    ///     println!("{}", std::ptr::read(y));
    /// }
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn write<T>(dst: *mut T, src: T) {
        intrinsics::move_val_init(&mut *dst, src)
    }

    /// Performs a volatile read of the value from `src` without moving it. This
    /// leaves the memory in `src` unchanged.
    ///
    /// Volatile operations are intended to act on I/O memory, and are guaranteed
    /// to not be elided or reordered by the compiler across other volatile
    /// operations.
    ///
    /// # Notes
    ///
    /// Rust does not currently have a rigorously and formally defined memory model,
    /// so the precise semantics of what "volatile" means here is subject to change
    /// over time. That being said, the semantics will almost always end up pretty
    /// similar to [C11's definition of volatile][c11].
    ///
    /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
    ///
    /// # Safety
    ///
    /// Beyond accepting a raw pointer, this is unsafe because it semantically
    /// moves the value out of `src` without preventing further usage of `src`.
    /// If `T` is not `Copy`, then care must be taken to ensure that the value at
    /// `src` is not used before the data is overwritten again (e.g. with `write`,
    /// `zero_memory`, or `copy_memory`). Note that `*src = foo` counts as a use
    /// because it will attempt to drop the value previously at `*src`.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let x = 12;
    /// let y = &x as *const i32;
    ///
    /// unsafe { println!("{}", std::ptr::read_volatile(y)); }
    /// ```
    #[inline]
    #[stable(feature = "volatile", since = "1.9.0")]
    pub unsafe fn read_volatile<T>(src: *const T) -> T {
        intrinsics::volatile_load(src)
    }

    /// Performs a volatile write of a memory location with the given value without
    /// reading or dropping the old value.
    ///
    /// Volatile operations are intended to act on I/O memory, and are guaranteed
    /// to not be elided or reordered by the compiler across other volatile
    /// operations.
    ///
    /// # Notes
    ///
    /// Rust does not currently have a rigorously and formally defined memory model,
    /// so the precise semantics of what "volatile" means here is subject to change
    /// over time. That being said, the semantics will almost always end up pretty
    /// similar to [C11's definition of volatile][c11].
    ///
    /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
    ///
    /// # Safety
    ///
    /// This operation is marked unsafe because it accepts a raw pointer.
    ///
    /// It does not drop the contents of `dst`. This is safe, but it could leak
    /// allocations or resources, so care must be taken not to overwrite an object
    /// that should be dropped.
    ///
    /// This is appropriate for initializing uninitialized memory, or overwriting
    /// memory that has previously been `read` from.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let mut x = 0;
    /// let y = &mut x as *mut i32;
    /// let z = 12;
    ///
    /// unsafe {
    ///     std::ptr::write_volatile(y, z);
    ///     println!("{}", std::ptr::read_volatile(y));
    /// }
    /// ```
    #[inline]
    #[stable(feature = "volatile", since = "1.9.0")]
    pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
        intrinsics::volatile_store(dst, src);
    }

    #[lang = "const_ptr"]
    impl<T: ?Sized> *const T {
        /// Returns true if the pointer is null.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s: &str = "Follow the rabbit";
        /// let ptr: *const u8 = s.as_ptr();
        /// assert!(!ptr.is_null());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn is_null(self) -> bool where T: Sized {
            self == null()
        }

        /// Returns `None` if the pointer is null, or else returns a reference to
        /// the value wrapped in `Some`.
        ///
        /// # Safety
        ///
        /// While this method and its mutable counterpart are useful for
        /// null-safety, it is important to note that this is still an unsafe
        /// operation because the returned value could be pointing to invalid
        /// memory.
        ///
        /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does
        /// not necessarily reflect the actual lifetime of the data.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```ignore
        /// let val: *const u8 = &10u8 as *const u8;
        ///
        /// unsafe {
        ///     if let Some(val_back) = val.as_ref() {
        ///         println!("We got back the value: {}!", val_back);
        ///     }
        /// }
        /// ```
        #[stable(feature = "ptr_as_ref", since = "1.9.0")]
        #[inline]
        pub unsafe fn as_ref<'a>(self) -> Option<&'a T> where T: Sized {
            if self.is_null() {
                None
            } else {
                Some(&*self)
            }
        }

        /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
        /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
        ///
        /// # Safety
        ///
        /// Both the starting and resulting pointer must be either in bounds or one
        /// byte past the end of an allocated object. If either pointer is out of
        /// bounds or arithmetic overflow occurs then
        /// any further use of the returned value will result in undefined behavior.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let s: &str = "123";
        /// let ptr: *const u8 = s.as_ptr();
        ///
        /// unsafe {
        ///     println!("{}", *ptr.offset(1) as char);
        ///     println!("{}", *ptr.offset(2) as char);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub unsafe fn offset(self, count: isize) -> *const T where T: Sized {
            intrinsics::offset(self, count)
        }
    }

    #[lang = "mut_ptr"]
    impl<T: ?Sized> *mut T {
        /// Returns true if the pointer is null.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut s = [1, 2, 3];
        /// let ptr: *mut u32 = s.as_mut_ptr();
        /// assert!(!ptr.is_null());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn is_null(self) -> bool where T: Sized {
            self == null_mut()
        }

        /// Returns `None` if the pointer is null, or else returns a reference to
        /// the value wrapped in `Some`.
        ///
        /// # Safety
        ///
        /// While this method and its mutable counterpart are useful for
        /// null-safety, it is important to note that this is still an unsafe
        /// operation because the returned value could be pointing to invalid
        /// memory.
        ///
        /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does
        /// not necessarily reflect the actual lifetime of the data.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```ignore
        /// let val: *mut u8 = &mut 10u8 as *mut u8;
        ///
        /// unsafe {
        ///     if let Some(val_back) = val.as_ref() {
        ///         println!("We got back the value: {}!", val_back);
        ///     }
        /// }
        /// ```
        #[stable(feature = "ptr_as_ref", since = "1.9.0")]
        #[inline]
        pub unsafe fn as_ref<'a>(self) -> Option<&'a T> where T: Sized {
            if self.is_null() {
                None
            } else {
                Some(&*self)
            }
        }

        /// Calculates the offset from a pointer. `count` is in units of T; e.g. a
        /// `count` of 3 represents a pointer offset of `3 * sizeof::<T>()` bytes.
        ///
        /// # Safety
        ///
        /// The offset must be in-bounds of the object, or one-byte-past-the-end.
        /// Otherwise `offset` invokes Undefined Behavior, regardless of whether
        /// the pointer is used.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut s = [1, 2, 3];
        /// let ptr: *mut u32 = s.as_mut_ptr();
        ///
        /// unsafe {
        ///     println!("{}", *ptr.offset(1));
        ///     println!("{}", *ptr.offset(2));
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub unsafe fn offset(self, count: isize) -> *mut T where T: Sized {
            intrinsics::offset(self, count) as *mut T
        }

        /// Returns `None` if the pointer is null, or else returns a mutable
        /// reference to the value wrapped in `Some`.
        ///
        /// # Safety
        ///
        /// As with `as_ref`, this is unsafe because it cannot verify the validity
        /// of the returned pointer, nor can it ensure that the lifetime `'a`
        /// returned is indeed a valid lifetime for the contained data.
        ///
        /// # Examples
        ///
        /// Basic usage:
        ///
        /// ```
        /// let mut s = [1, 2, 3];
        /// let ptr: *mut u32 = s.as_mut_ptr();
        /// let first_value = unsafe { ptr.as_mut().unwrap() };
        /// *first_value = 4;
        /// println!("{:?}", s); // It'll print: "[4, 2, 3]".
        /// ```
        #[stable(feature = "ptr_as_ref", since = "1.9.0")]
        #[inline]
        pub unsafe fn as_mut<'a>(self) -> Option<&'a mut T> where T: Sized {
            if self.is_null() {
                None
            } else {
                Some(&mut *self)
            }
        }
    }

    // Equality for pointers
    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> PartialEq for *const T {
        #[inline]
        fn eq(&self, other: &*const T) -> bool { *self == *other }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Eq for *const T {}

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> PartialEq for *mut T {
        #[inline]
        fn eq(&self, other: &*mut T) -> bool { *self == *other }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Eq for *mut T {}

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Clone for *const T {
        #[inline]
        fn clone(&self) -> *const T {
            *self
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Clone for *mut T {
        #[inline]
        fn clone(&self) -> *mut T {
            *self
        }
    }

    // Impls for function pointers
    macro_rules! fnptr_impls_safety_abi {
        ($FnTy: ty, $($Arg: ident),*) => {
            #[stable(feature = "rust1", since = "1.0.0")]
            impl<Ret, $($Arg),*> Clone for $FnTy {
                #[inline]
                fn clone(&self) -> Self {
                    *self
                }
            }

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> PartialEq for $FnTy {
                #[inline]
                fn eq(&self, other: &Self) -> bool {
                    *self as usize == *other as usize
                }
            }

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> Eq for $FnTy {}

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> PartialOrd for $FnTy {
                #[inline]
                fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
                    (*self as usize).partial_cmp(&(*other as usize))
                }
            }

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> Ord for $FnTy {
                #[inline]
                fn cmp(&self, other: &Self) -> Ordering {
                    (*self as usize).cmp(&(*other as usize))
                }
            }

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> hash::Hash for $FnTy {
                fn hash<HH: hash::Hasher>(&self, state: &mut HH) {
                    state.write_usize(*self as usize)
                }
            }

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> fmt::Pointer for $FnTy {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    fmt::Pointer::fmt(&(*self as *const ()), f)
                }
            }

            #[stable(feature = "fnptr_impls", since = "1.4.0")]
            impl<Ret, $($Arg),*> fmt::Debug for $FnTy {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    fmt::Pointer::fmt(&(*self as *const ()), f)
                }
            }
        }
    }

    macro_rules! fnptr_impls_args {
        ($($Arg: ident),+) => {
            fnptr_impls_safety_abi! { extern "Rust" fn($($Arg),*) -> Ret, $($Arg),* }
            fnptr_impls_safety_abi! { extern "C" fn($($Arg),*) -> Ret, $($Arg),* }
            fnptr_impls_safety_abi! { extern "C" fn($($Arg),* , ...) -> Ret, $($Arg),* }
            fnptr_impls_safety_abi! { unsafe extern "Rust" fn($($Arg),*) -> Ret, $($Arg),* }
            fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),*) -> Ret, $($Arg),* }
            fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),* , ...) -> Ret, $($Arg),* }
        };
        () => {
            // No variadic functions with 0 parameters
            fnptr_impls_safety_abi! { extern "Rust" fn() -> Ret, }
            fnptr_impls_safety_abi! { extern "C" fn() -> Ret, }
            fnptr_impls_safety_abi! { unsafe extern "Rust" fn() -> Ret, }
            fnptr_impls_safety_abi! { unsafe extern "C" fn() -> Ret, }
        };
    }

    fnptr_impls_args! { }
    fnptr_impls_args! { A }
    fnptr_impls_args! { A, B }
    fnptr_impls_args! { A, B, C }
    fnptr_impls_args! { A, B, C, D }
    fnptr_impls_args! { A, B, C, D, E }
    fnptr_impls_args! { A, B, C, D, E, F }
    fnptr_impls_args! { A, B, C, D, E, F, G }
    fnptr_impls_args! { A, B, C, D, E, F, G, H }
    fnptr_impls_args! { A, B, C, D, E, F, G, H, I }
    fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J }
    fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K }
    fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L }

    // Comparison for pointers
    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Ord for *const T {
        #[inline]
        fn cmp(&self, other: &*const T) -> Ordering {
            if self < other {
                Less
            } else if self == other {
                Equal
            } else {
                Greater
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> PartialOrd for *const T {
        #[inline]
        fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
            Some(self.cmp(other))
        }

        #[inline]
        fn lt(&self, other: &*const T) -> bool { *self < *other }

        #[inline]
        fn le(&self, other: &*const T) -> bool { *self <= *other }

        #[inline]
        fn gt(&self, other: &*const T) -> bool { *self > *other }

        #[inline]
        fn ge(&self, other: &*const T) -> bool { *self >= *other }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Ord for *mut T {
        #[inline]
        fn cmp(&self, other: &*mut T) -> Ordering {
            if self < other {
                Less
            } else if self == other {
                Equal
            } else {
                Greater
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> PartialOrd for *mut T {
        #[inline]
        fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
            Some(self.cmp(other))
        }

        #[inline]
        fn lt(&self, other: &*mut T) -> bool { *self < *other }

        #[inline]
        fn le(&self, other: &*mut T) -> bool { *self <= *other }

        #[inline]
        fn gt(&self, other: &*mut T) -> bool { *self > *other }

        #[inline]
        fn ge(&self, other: &*mut T) -> bool { *self >= *other }
    }

    /// A wrapper around a raw non-null `*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).  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.
    #[allow(missing_debug_implementations)]
    #[unstable(feature = "unique", reason = "needs an RFC to flesh out design",
               issue = "27730")]
    pub struct Unique<T: ?Sized> {
        pointer: NonZero<*const T>,
        // NOTE: this marker has no consequences for variance, but is necessary
        // for dropck to understand that we logically own a `T`.
        //
        // For details, see:
        // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
        _marker: PhantomData<T>,
    }

    /// `Unique` pointers are `Send` if `T` is `Send` because the data they
    /// reference is unaliased. Note that this aliasing invariant is
    /// unenforced by the type system; the abstraction using the
    /// `Unique` must enforce it.
    #[unstable(feature = "unique", issue = "27730")]
    unsafe impl<T: Send + ?Sized> Send for Unique<T> { }

    /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
    /// reference is unaliased. Note that this aliasing invariant is
    /// unenforced by the type system; the abstraction using the
    /// `Unique` must enforce it.
    #[unstable(feature = "unique", issue = "27730")]
    unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { }

    #[unstable(feature = "unique", issue = "27730")]
    impl<T: ?Sized> Unique<T> {
        /// Creates a new `Unique`.
        ///
        /// # Safety
        ///
        /// `ptr` must be non-null.
        pub const unsafe fn new(ptr: *mut T) -> Unique<T> {
            Unique { pointer: NonZero::new(ptr), _marker: PhantomData }
        }

        /// Dereferences the content.
        pub unsafe fn get(&self) -> &T {
            &**self.pointer
        }

        /// Mutably dereferences the content.
        pub unsafe fn get_mut(&mut self) -> &mut T {
            &mut ***self
        }
    }

    #[unstable(feature = "unique", issue = "27730")]
    impl<T: ?Sized, U: ?Sized> CoerceUnsized<Unique<U>> for Unique<T> where T: Unsize<U> { }

    #[unstable(feature = "unique", issue= "27730")]
    impl<T:?Sized> Deref for Unique<T> {
        type Target = *mut T;

        #[inline]
        fn deref(&self) -> &*mut T {
            unsafe { mem::transmute(&*self.pointer) }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T> fmt::Pointer for Unique<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Pointer::fmt(&*self.pointer, f)
        }
    }

    /// A wrapper around a raw non-null `*mut T` that indicates that the possessor
    /// of this wrapper has shared ownership of the referent. Useful for
    /// building abstractions like `Rc<T>` or `Arc<T>`, which internally
    /// use raw pointers to manage the memory that they own.
    #[allow(missing_debug_implementations)]
    #[unstable(feature = "shared", reason = "needs an RFC to flesh out design",
               issue = "27730")]
    pub struct Shared<T: ?Sized> {
        pointer: NonZero<*const T>,
        // NOTE: this marker has no consequences for variance, but is necessary
        // for dropck to understand that we logically own a `T`.
        //
        // For details, see:
        // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
        _marker: PhantomData<T>,
    }

    /// `Shared` pointers are not `Send` because the data they reference may be aliased.
    // NB: This impl is unnecessary, but should provide better error messages.
    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized> !Send for Shared<T> { }

    /// `Shared` pointers are not `Sync` because the data they reference may be aliased.
    // NB: This impl is unnecessary, but should provide better error messages.
    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized> !Sync for Shared<T> { }

    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized> Shared<T> {
        /// Creates a new `Shared`.
        ///
        /// # Safety
        ///
        /// `ptr` must be non-null.
        pub unsafe fn new(ptr: *mut T) -> Self {
            Shared { pointer: NonZero::new(ptr), _marker: PhantomData }
        }
    }

    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized> Clone for Shared<T> {
        fn clone(&self) -> Self {
            *self
        }
    }

    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized> Copy for Shared<T> { }

    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized, U: ?Sized> CoerceUnsized<Shared<U>> for Shared<T> where T: Unsize<U> { }

    #[unstable(feature = "shared", issue = "27730")]
    impl<T: ?Sized> Deref for Shared<T> {
        type Target = *mut T;

        #[inline]
        fn deref(&self) -> &*mut T {
            unsafe { mem::transmute(&*self.pointer) }
        }
    }

    #[unstable(feature = "shared", issue = "27730")]
    impl<T> fmt::Pointer for Shared<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Pointer::fmt(&*self.pointer, f)
        }
    }

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