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    use core::fmt;
    use core::mem::MaybeUninit;
    use core::ops::{
        Index, IndexMut, Range, RangeFrom, RangeFull, RangeInclusive, RangeTo, RangeToInclusive,
    };

    /// Uninitialized byte slice.
    ///
    /// Returned by `BufMut::chunk_mut()`, the referenced byte slice may be
    /// uninitialized. The wrapper provides safe access without introducing
    /// undefined behavior.
    ///
    /// The safety invariants of this wrapper are:
    ///
    ///  1. Reading from an `UninitSlice` is undefined behavior.
    ///  2. Writing uninitialized bytes to an `UninitSlice` is undefined behavior.
    ///
    /// The difference between `&mut UninitSlice` and `&mut [MaybeUninit<u8>]` is
    /// that it is possible in safe code to write uninitialized bytes to an
    /// `&mut [MaybeUninit<u8>]`, which this type prohibits.
    #[repr(transparent)]
    pub struct UninitSlice([MaybeUninit<u8>]);

    impl UninitSlice {
        /// Creates a `&mut UninitSlice` wrapping a slice of initialised memory.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::buf::UninitSlice;
        ///
        /// let mut buffer = [0u8; 64];
        /// let slice = UninitSlice::new(&mut buffer[..]);
        /// ```
        #[inline]
        pub fn new(slice: &mut [u8]) -> &mut UninitSlice {
            unsafe { &mut *(slice as *mut [u8] as *mut [MaybeUninit<u8>] as *mut UninitSlice) }
        }

        /// Creates a `&mut UninitSlice` wrapping a slice of uninitialised memory.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::buf::UninitSlice;
        /// use core::mem::MaybeUninit;
        ///
        /// let mut buffer = [MaybeUninit::uninit(); 64];
        /// let slice = UninitSlice::uninit(&mut buffer[..]);
        ///
        /// let mut vec = Vec::with_capacity(1024);
        /// let spare: &mut UninitSlice = vec.spare_capacity_mut().into();
        /// ```
        #[inline]
        pub fn uninit(slice: &mut [MaybeUninit<u8>]) -> &mut UninitSlice {
            unsafe { &mut *(slice as *mut [MaybeUninit<u8>] as *mut UninitSlice) }
        }

        fn uninit_ref(slice: &[MaybeUninit<u8>]) -> &UninitSlice {
            unsafe { &*(slice as *const [MaybeUninit<u8>] as *const UninitSlice) }
        }

        /// Create a `&mut UninitSlice` from a pointer and a length.
        ///
        /// # Safety
        ///
        /// The caller must ensure that `ptr` references a valid memory region owned
        /// by the caller representing a byte slice for the duration of `'a`.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::buf::UninitSlice;
        ///
        /// let bytes = b"hello world".to_vec();
        /// let ptr = bytes.as_ptr() as *mut _;
        /// let len = bytes.len();
        ///
        /// let slice = unsafe { UninitSlice::from_raw_parts_mut(ptr, len) };
        /// ```
        #[inline]
        pub unsafe fn from_raw_parts_mut<'a>(ptr: *mut u8, len: usize) -> &'a mut UninitSlice {
            let maybe_init: &mut [MaybeUninit<u8>] =
                core::slice::from_raw_parts_mut(ptr as *mut _, len);
            Self::uninit(maybe_init)
        }

        /// Write a single byte at the specified offset.
        ///
        /// # Panics
        ///
        /// The function panics if `index` is out of bounds.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::buf::UninitSlice;
        ///
        /// let mut data = [b'f', b'o', b'o'];
        /// let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) };
        ///
        /// slice.write_byte(0, b'b');
        ///
        /// assert_eq!(b"boo", &data[..]);
        /// ```
        #[inline]
        pub fn write_byte(&mut self, index: usize, byte: u8) {
            assert!(index < self.len());

            unsafe { self[index..].as_mut_ptr().write(byte) }
        }

        /// Copies bytes from `src` into `self`.
        ///
        /// The length of `src` must be the same as `self`.
        ///
        /// # Panics
        ///
        /// The function panics if `src` has a different length than `self`.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::buf::UninitSlice;
        ///
        /// let mut data = [b'f', b'o', b'o'];
        /// let slice = unsafe { UninitSlice::from_raw_parts_mut(data.as_mut_ptr(), 3) };
        ///
        /// slice.copy_from_slice(b"bar");
        ///
        /// assert_eq!(b"bar", &data[..]);
        /// ```
        #[inline]
        pub fn copy_from_slice(&mut self, src: &[u8]) {
            use core::ptr;

            assert_eq!(self.len(), src.len());

            unsafe {
                ptr::copy_nonoverlapping(src.as_ptr(), self.as_mut_ptr(), self.len());
            }
        }

        /// Return a raw pointer to the slice's buffer.
        ///
        /// # Safety
        ///
        /// The caller **must not** read from the referenced memory and **must not**
        /// write **uninitialized** bytes to the slice either.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::BufMut;
        ///
        /// let mut data = [0, 1, 2];
        /// let mut slice = &mut data[..];
        /// let ptr = BufMut::chunk_mut(&mut slice).as_mut_ptr();
        /// ```
        #[inline]
        pub fn as_mut_ptr(&mut self) -> *mut u8 {
            self.0.as_mut_ptr() as *mut _
        }

        /// Return a `&mut [MaybeUninit<u8>]` to this slice's buffer.
        ///
        /// # Safety
        ///
        /// The caller **must not** read from the referenced memory and **must not** write
        /// **uninitialized** bytes to the slice either. This is because `BufMut` implementation
        /// that created the `UninitSlice` knows which parts are initialized. Writing uninitialized
        /// bytes to the slice may cause the `BufMut` to read those bytes and trigger undefined
        /// behavior.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::BufMut;
        ///
        /// let mut data = [0, 1, 2];
        /// let mut slice = &mut data[..];
        /// unsafe {
        ///     let uninit_slice = BufMut::chunk_mut(&mut slice).as_uninit_slice_mut();
        /// };
        /// ```
        #[inline]
        pub unsafe fn as_uninit_slice_mut(&mut self) -> &mut [MaybeUninit<u8>] {
            &mut self.0
        }

        /// Returns the number of bytes in the slice.
        ///
        /// # Examples
        ///
        /// ```
        /// use bytes::BufMut;
        ///
        /// let mut data = [0, 1, 2];
        /// let mut slice = &mut data[..];
        /// let len = BufMut::chunk_mut(&mut slice).len();
        ///
        /// assert_eq!(len, 3);
        /// ```
        #[inline]
        pub fn len(&self) -> usize {
            self.0.len()
        }
    }

    impl fmt::Debug for UninitSlice {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt.debug_struct("UninitSlice[...]").finish()
        }
    }

    impl<'a> From<&'a mut [u8]> for &'a mut UninitSlice {
        fn from(slice: &'a mut [u8]) -> Self {
            UninitSlice::new(slice)
        }
    }

    impl<'a> From<&'a mut [MaybeUninit<u8>]> for &'a mut UninitSlice {
        fn from(slice: &'a mut [MaybeUninit<u8>]) -> Self {
            UninitSlice::uninit(slice)
        }
    }

    macro_rules! impl_index {
        ($($t:ty),*) => {
            $(
                impl Index<$t> for UninitSlice {
                    type Output = UninitSlice;

                    #[inline]
                    fn index(&self, index: $t) -> &UninitSlice {
                        UninitSlice::uninit_ref(&self.0[index])
                    }
                }

                impl IndexMut<$t> for UninitSlice {
                    #[inline]
                    fn index_mut(&mut self, index: $t) -> &mut UninitSlice {
                        UninitSlice::uninit(&mut self.0[index])
                    }
                }
            )*
        };
    }

    impl_index!(
        Range<usize>,
        RangeFrom<usize>,
        RangeFull,
        RangeInclusive<usize>,
        RangeTo<usize>,
        RangeToInclusive<usize>
    );