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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.

    //! Exposes the NonZero lang item which provides optimization hints.
    #![unstable(feature = "nonzero",
                reason = "needs an RFC to flesh out the design",
                issue = "27730")]

    use ops::CoerceUnsized;

    /// Unsafe trait to indicate what types are usable with the NonZero struct
    pub unsafe trait Zeroable {
        /// Whether this value is zero
        fn is_zero(&self) -> bool;
    }

    macro_rules! impl_zeroable_for_pointer_types {
        ( $( $Ptr: ty )+ ) => {
            $(
                /// For fat pointers to be considered "zero", only the "data" part needs to be null.
                unsafe impl<T: ?Sized> Zeroable for $Ptr {
                    #[inline]
                    fn is_zero(&self) -> bool {
                        // Cast because `is_null` is only available on thin pointers
                        (*self as *mut u8).is_null()
                    }
                }
            )+
        }
    }

    macro_rules! impl_zeroable_for_integer_types {
        ( $( $Int: ty )+ ) => {
            $(
                unsafe impl Zeroable for $Int {
                    #[inline]
                    fn is_zero(&self) -> bool {
                        *self == 0
                    }
                }
            )+
        }
    }

    impl_zeroable_for_pointer_types! {
        *const T
        *mut T
    }

    impl_zeroable_for_integer_types! {
        usize u8 u16 u32 u64 u128
        isize i8 i16 i32 i64 i128
    }

    /// A wrapper type for raw pointers and integers that will never be
    /// NULL or 0 that might allow certain optimizations.
    #[lang = "non_zero"]
    #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Hash)]
    pub struct NonZero<T: Zeroable>(T);

    impl<T: Zeroable> NonZero<T> {
        /// Creates an instance of NonZero with the provided value.
        /// You must indeed ensure that the value is actually "non-zero".
        #[unstable(feature = "nonzero",
                   reason = "needs an RFC to flesh out the design",
                   issue = "27730")]
        #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_nonzero_new"))]
        #[inline]
        pub const unsafe fn new_unchecked(inner: T) -> Self {
            NonZero(inner)
        }

        /// Creates an instance of NonZero with the provided value.
        #[inline]
        pub fn new(inner: T) -> Option<Self> {
            if inner.is_zero() {
                None
            } else {
                Some(NonZero(inner))
            }
        }

        /// Gets the inner value.
        pub fn get(self) -> T {
            self.0
        }
    }

    impl<T: Zeroable+CoerceUnsized<U>, U: Zeroable> CoerceUnsized<NonZero<U>> for NonZero<T> {}

    impl<'a, T: ?Sized> From<&'a mut T> for NonZero<*mut T> {
        fn from(reference: &'a mut T) -> Self {
            NonZero(reference)
        }
    }

    impl<'a, T: ?Sized> From<&'a mut T> for NonZero<*const T> {
        fn from(reference: &'a mut T) -> Self {
            let ptr: *mut T = reference;
            NonZero(ptr)
        }
    }

    impl<'a, T: ?Sized> From<&'a T> for NonZero<*const T> {
        fn from(reference: &'a T) -> Self {
            NonZero(reference)
        }
    }

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