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    //! Types which pin data to its location in memory
    //!
    //! See the [standard library module] for more information.
    //!
    //! [standard library module]: ../../std/pin/index.html

    #![unstable(feature = "pin", issue = "49150")]

    use fmt;
    use future::{Future, UnsafeFutureObj};
    use marker::{Sized, Unpin, Unsize};
    use task::{Context, Poll};
    use ops::{Deref, DerefMut, CoerceUnsized};

    /// A pinned reference.
    ///
    /// This type is similar to a mutable reference, except that it pins its value,
    /// which prevents it from moving out of the reference, unless it implements [`Unpin`].
    ///
    /// See the [`pin` module] documentation for furthur explanation on pinning.
    ///
    /// [`Unpin`]: ../../std/marker/trait.Unpin.html
    /// [`pin` module]: ../../std/pin/index.html
    #[unstable(feature = "pin", issue = "49150")]
    #[fundamental]
    pub struct PinMut<'a, T: ?Sized + 'a> {
        inner: &'a mut T,
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized + Unpin> PinMut<'a, T> {
        /// Construct a new `PinMut` around a reference to some data of a type that
        /// implements `Unpin`.
        #[unstable(feature = "pin", issue = "49150")]
        pub fn new(reference: &'a mut T) -> PinMut<'a, T> {
            PinMut { inner: reference }
        }

        /// Get a mutable reference to the data inside of this `PinMut`.
        #[unstable(feature = "pin", issue = "49150")]
        pub fn get_mut(this: PinMut<'a, T>) -> &'a mut T {
            this.inner
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized> PinMut<'a, T> {
        /// Construct a new `PinMut` around a reference to some data of a type that
        /// may or may not implement `Unpin`.
        ///
        /// This constructor is unsafe because we do not know what will happen with
        /// that data after the lifetime of the reference ends. If you cannot guarantee that the
        /// data will never move again, calling this constructor is invalid.
        #[unstable(feature = "pin", issue = "49150")]
        pub unsafe fn new_unchecked(reference: &'a mut T) -> PinMut<'a, T> {
            PinMut { inner: reference }
        }

        /// Reborrow a `PinMut` for a shorter lifetime.
        ///
        /// For example, `PinMut::get_mut(x.reborrow())` (unsafely) returns a
        /// short-lived mutable reference reborrowing from `x`.
        #[unstable(feature = "pin", issue = "49150")]
        pub fn reborrow<'b>(&'b mut self) -> PinMut<'b, T> {
            PinMut { inner: self.inner }
        }

        /// Get a mutable reference to the data inside of this `PinMut`.
        ///
        /// This function is unsafe. You must guarantee that you will never move
        /// the data out of the mutable reference you receive when you call this
        /// function.
        #[unstable(feature = "pin", issue = "49150")]
        pub unsafe fn get_mut_unchecked(this: PinMut<'a, T>) -> &'a mut T {
            this.inner
        }

        /// Construct a new pin by mapping the interior value.
        ///
        /// For example, if you  wanted to get a `PinMut` of a field of something,
        /// you could use this to get access to that field in one line of code.
        ///
        /// This function is unsafe. You must guarantee that the data you return
        /// will not move so long as the argument value does not move (for example,
        /// because it is one of the fields of that value), and also that you do
        /// not move out of the argument you receive to the interior function.
        #[unstable(feature = "pin", issue = "49150")]
        pub unsafe fn map_unchecked<U, F>(this: PinMut<'a, T>, f: F) -> PinMut<'a, U> where
            F: FnOnce(&mut T) -> &mut U
        {
            PinMut { inner: f(this.inner) }
        }

        /// Assign a new value to the memory behind the pinned reference.
        #[unstable(feature = "pin", issue = "49150")]
        pub fn set(this: PinMut<'a, T>, value: T)
            where T: Sized,
        {
            *this.inner = value;
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized> Deref for PinMut<'a, T> {
        type Target = T;

        fn deref(&self) -> &T {
            &*self.inner
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized + Unpin> DerefMut for PinMut<'a, T> {
        fn deref_mut(&mut self) -> &mut T {
            self.inner
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: fmt::Debug + ?Sized> fmt::Debug for PinMut<'a, T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Debug::fmt(&**self, f)
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: fmt::Display + ?Sized> fmt::Display for PinMut<'a, T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Display::fmt(&**self, f)
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized> fmt::Pointer for PinMut<'a, T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Pointer::fmt(&(&*self.inner as *const T), f)
        }
    }

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PinMut<'a, U>> for PinMut<'a, T> {}

    #[unstable(feature = "pin", issue = "49150")]
    impl<'a, T: ?Sized> Unpin for PinMut<'a, T> {}

    #[unstable(feature = "futures_api", issue = "50547")]
    unsafe impl<'a, T, F> UnsafeFutureObj<'a, T> for PinMut<'a, F>
        where F: Future<Output = T> + 'a
    {
        fn into_raw(self) -> *mut () {
            unsafe { PinMut::get_mut_unchecked(self) as *mut F as *mut () }
        }

        unsafe fn poll(ptr: *mut (), cx: &mut Context) -> Poll<T> {
            PinMut::new_unchecked(&mut *(ptr as *mut F)).poll(cx)
        }

        unsafe fn drop(_ptr: *mut ()) {}
    }

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