bytes.rs

        if let Some(0) = upper {
            return;
        }

        let mut bytes_mut = match mem::replace(self, Bytes::new()).try_mut() {
            Ok(bytes_mut) => bytes_mut,
            Err(bytes) => {
                let mut bytes_mut = BytesMut::with_capacity(bytes.len() + lower);
                bytes_mut.put_slice(&bytes);
                bytes_mut
            }
        };

        bytes_mut.extend(iter);

        mem::replace(self, bytes_mut.freeze());
    }
}

impl<'a> Extend<&'a u8> for Bytes {
    fn extend<T>(&mut self, iter: T) where T: IntoIterator<Item = &'a u8> {
        self.extend(iter.into_iter().map(|b| *b))
    }
}

/*
 *
 * ===== BytesMut =====
 *
 */

impl BytesMut {
    /// Creates a new `BytesMut` with the specified capacity.
    ///
    /// The returned `BytesMut` will be able to hold at least `capacity` bytes
    /// without reallocating. If `capacity` is under `4 * size_of::<usize>() - 1`,
    /// then `BytesMut` will not allocate.
    ///
    /// It is important to note that this function does not specify the length
    /// of the returned `BytesMut`, but only the capacity.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut bytes = BytesMut::with_capacity(64);
    ///
    /// // `bytes` contains no data, even though there is capacity
    /// assert_eq!(bytes.len(), 0);
    ///
    /// bytes.put(&b"hello world"[..]);
    ///
    /// assert_eq!(&bytes[..], b"hello world");
    /// ```
    #[inline]
    pub fn with_capacity(capacity: usize) -> BytesMut {
        BytesMut {
            inner: Inner::with_capacity(capacity),
        }
    }

    /// Creates a new `BytesMut` with default capacity.
    ///
    /// Resulting object has length 0 and unspecified capacity.
    /// This function does not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut bytes = BytesMut::new();
    ///
    /// assert_eq!(0, bytes.len());
    ///
    /// bytes.reserve(2);
    /// bytes.put_slice(b"xy");
    ///
    /// assert_eq!(&b"xy"[..], &bytes[..]);
    /// ```
    #[inline]
    pub fn new() -> BytesMut {
        BytesMut::with_capacity(0)
    }

    /// Returns the number of bytes contained in this `BytesMut`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::from(&b"hello"[..]);
    /// assert_eq!(b.len(), 5);
    /// ```
    #[inline]
    pub fn len(&self) -> usize {
        self.inner.len()
    }

    /// Returns true if the `BytesMut` has a length of 0.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::with_capacity(64);
    /// assert!(b.is_empty());
    /// ```
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Returns the number of bytes the `BytesMut` can hold without reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::with_capacity(64);
    /// assert_eq!(b.capacity(), 64);
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.inner.capacity()
    }

    /// Converts `self` into an immutable `Bytes`.
    ///
    /// The conversion is zero cost and is used to indicate that the slice
    /// referenced by the handle will no longer be mutated. Once the conversion
    /// is done, the handle can be cloned and shared across threads.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    /// use std::thread;
    ///
    /// let mut b = BytesMut::with_capacity(64);
    /// b.put("hello world");
    /// let b1 = b.freeze();
    /// let b2 = b1.clone();
    ///
    /// let th = thread::spawn(move || {
    ///     assert_eq!(&b1[..], b"hello world");
    /// });
    ///
    /// assert_eq!(&b2[..], b"hello world");
    /// th.join().unwrap();
    /// ```
    #[inline]
    pub fn freeze(self) -> Bytes {
        Bytes { inner: self.inner }
    }

    /// Splits the bytes into two at the given index.
    ///
    /// Afterwards `self` contains elements `[0, at)`, and the returned
    /// `BytesMut` contains elements `[at, capacity)`.
    ///
    /// This is an `O(1)` operation that just increases the reference count
    /// and sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut a = BytesMut::from(&b"hello world"[..]);
    /// let mut b = a.split_off(5);
    ///
    /// a[0] = b'j';
    /// b[0] = b'!';
    ///
    /// assert_eq!(&a[..], b"jello");
    /// assert_eq!(&b[..], b"!world");
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if `at > capacity`.
    pub fn split_off(&mut self, at: usize) -> BytesMut {
        BytesMut {
            inner: self.inner.split_off(at),
        }
    }

    /// Removes the bytes from the current view, returning them in a new
    /// `BytesMut` handle.
    ///
    /// Afterwards, `self` will be empty, but will retain any additional
    /// capacity that it had before the operation. This is identical to
    /// `self.split_to(self.len())`.
    ///
    /// This is an `O(1)` operation that just increases the reference count and
    /// sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut buf = BytesMut::with_capacity(1024);
    /// buf.put(&b"hello world"[..]);
    ///
    /// let other = buf.take();
    ///
    /// assert!(buf.is_empty());
    /// assert_eq!(1013, buf.capacity());
    ///
    /// assert_eq!(other, b"hello world"[..]);
    /// ```
    pub fn take(&mut self) -> BytesMut {
        let len = self.len();
        self.split_to(len)
    }

    #[deprecated(since = "0.4.1", note = "use take instead")]
    #[doc(hidden)]
    pub fn drain(&mut self) -> BytesMut {
        self.take()
    }

    /// Splits the buffer into two at the given index.
    ///
    /// Afterwards `self` contains elements `[at, len)`, and the returned `BytesMut`
    /// contains elements `[0, at)`.
    ///
    /// This is an `O(1)` operation that just increases the reference count and
    /// sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut a = BytesMut::from(&b"hello world"[..]);
    /// let mut b = a.split_to(5);
    ///
    /// a[0] = b'!';
    /// b[0] = b'j';
    ///
    /// assert_eq!(&a[..], b"!world");
    /// assert_eq!(&b[..], b"jello");
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if `at > len`.
    pub fn split_to(&mut self, at: usize) -> BytesMut {
        BytesMut {
            inner: self.inner.split_to(at),
        }
    }

    #[deprecated(since = "0.4.1", note = "use split_to instead")]
    #[doc(hidden)]
    pub fn drain_to(&mut self, at: usize) -> BytesMut {
        self.split_to(at)
    }

    /// Shortens the buffer, keeping the first `len` bytes and dropping the
    /// rest.
    ///
    /// If `len` is greater than the buffer's current length, this has no
    /// effect.
    ///
    /// The [`split_off`] method can emulate `truncate`, but this causes the
    /// excess bytes to be returned instead of dropped.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello world"[..]);
    /// buf.truncate(5);
    /// assert_eq!(buf, b"hello"[..]);
    /// ```
    ///
    /// [`split_off`]: #method.split_off
    pub fn truncate(&mut self, len: usize) {
        self.inner.truncate(len);
    }

    /// Shortens the buffer, dropping the first `cnt` bytes and keeping the
    /// rest.
    ///
    /// This is the same function as `Buf::advance`, and in the next breaking
    /// release of `bytes`, this implementation will be removed in favor of
    /// having `BytesMut` implement `Buf`.
    ///
    /// # Panics
    ///
    /// This function panics if `cnt` is greater than `self.len()`
    #[inline]
    pub fn advance(&mut self, cnt: usize) {
        assert!(cnt <= self.len(), "cannot advance past `remaining`");
        unsafe { self.inner.set_start(cnt); }
    }

    /// Clears the buffer, removing all data.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello world"[..]);
    /// buf.clear();
    /// assert!(buf.is_empty());
    /// ```
    pub fn clear(&mut self) {
        self.truncate(0);
    }

    /// Resizes the buffer so that `len` is equal to `new_len`.
    ///
    /// If `new_len` is greater than `len`, the buffer is extended by the
    /// difference with each additional byte set to `value`. If `new_len` is
    /// less than `len`, the buffer is simply truncated.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::new();
    ///
    /// buf.resize(3, 0x1);
    /// assert_eq!(&buf[..], &[0x1, 0x1, 0x1]);
    ///
    /// buf.resize(2, 0x2);
    /// assert_eq!(&buf[..], &[0x1, 0x1]);
    ///
    /// buf.resize(4, 0x3);
    /// assert_eq!(&buf[..], &[0x1, 0x1, 0x3, 0x3]);
    /// ```
    pub fn resize(&mut self, new_len: usize, value: u8) {
        self.inner.resize(new_len, value);
    }

    /// Sets the length of the buffer.
    ///
    /// This will explicitly set the size of the buffer without actually
    /// modifying the data, so it is up to the caller to ensure that the data
    /// has been initialized.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut b = BytesMut::from(&b"hello world"[..]);
    ///
    /// unsafe {
    ///     b.set_len(5);
    /// }
    ///
    /// assert_eq!(&b[..], b"hello");
    ///
    /// unsafe {
    ///     b.set_len(11);
    /// }
    ///
    /// assert_eq!(&b[..], b"hello world");
    /// ```
    ///
    /// # Panics
    ///
    /// This method will panic if `len` is out of bounds for the underlying
    /// slice or if it comes after the `end` of the configured window.
    pub unsafe fn set_len(&mut self, len: usize) {
        self.inner.set_len(len)
    }

    /// Reserves capacity for at least `additional` more bytes to be inserted
    /// into the given `BytesMut`.
    ///
    /// More than `additional` bytes may be reserved in order to avoid frequent
    /// reallocations. A call to `reserve` may result in an allocation.
    ///
    /// Before allocating new buffer space, the function will attempt to reclaim
    /// space in the existing buffer. If the current handle references a small
    /// view in the original buffer and all other handles have been dropped,
    /// and the requested capacity is less than or equal to the existing
    /// buffer's capacity, then the current view will be copied to the front of
    /// the buffer and the handle will take ownership of the full buffer.
    ///
    /// # Examples
    ///
    /// In the following example, a new buffer is allocated.
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello"[..]);
    /// buf.reserve(64);
    /// assert!(buf.capacity() >= 69);
    /// ```
    ///
    /// In the following example, the existing buffer is reclaimed.
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut buf = BytesMut::with_capacity(128);
    /// buf.put(&[0; 64][..]);
    ///
    /// let ptr = buf.as_ptr();
    /// let other = buf.take();
    ///
    /// assert!(buf.is_empty());
    /// assert_eq!(buf.capacity(), 64);
    ///
    /// drop(other);
    /// buf.reserve(128);
    ///
    /// assert_eq!(buf.capacity(), 128);
    /// assert_eq!(buf.as_ptr(), ptr);
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    pub fn reserve(&mut self, additional: usize) {
        self.inner.reserve(additional)
    }

    /// Appends given bytes to this object.
    ///
    /// If this `BytesMut` object has not enough capacity, it is resized first.
    /// So unlike `put_slice` operation, `extend_from_slice` does not panic.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::with_capacity(0);
    /// buf.extend_from_slice(b"aaabbb");
    /// buf.extend_from_slice(b"cccddd");
    ///
    /// assert_eq!(b"aaabbbcccddd", &buf[..]);
    /// ```
    pub fn extend_from_slice(&mut self, extend: &[u8]) {
        self.reserve(extend.len());
        self.put_slice(extend);
    }

    /// Combine splitted BytesMut objects back as contiguous.
    ///
    /// If `BytesMut` objects were not contiguous originally, they will be extended.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::with_capacity(64);
    /// buf.extend_from_slice(b"aaabbbcccddd");
    ///
    /// let splitted = buf.split_off(6);
    /// assert_eq!(b"aaabbb", &buf[..]);
    /// assert_eq!(b"cccddd", &splitted[..]);
    ///
    /// buf.unsplit(splitted);
    /// assert_eq!(b"aaabbbcccddd", &buf[..]);
    /// ```
    pub fn unsplit(&mut self, other: BytesMut) {
        let ptr;

        if other.is_empty() {
            return;
        }

        if self.is_empty() {
            *self = other;
            return;
        }

        unsafe {
            ptr = self.inner.ptr.offset(self.inner.len as isize); 
        }
        if ptr == other.inner.ptr &&
           self.inner.kind() == KIND_ARC &&
           other.inner.kind() == KIND_ARC
        {
            debug_assert_eq!(self.inner.arc.load(Acquire),
                             other.inner.arc.load(Acquire));
            // Contiguous blocks, just combine directly
            self.inner.len += other.inner.len;
            self.inner.cap += other.inner.cap;
        }
        else {
            self.extend_from_slice(&other);
        }
    }
}

impl BufMut for BytesMut {
    #[inline]
    fn remaining_mut(&self) -> usize {
        self.capacity() - self.len()
    }

    #[inline]
    unsafe fn advance_mut(&mut self, cnt: usize) {
        let new_len = self.len() + cnt;

        // This call will panic if `cnt` is too big
        self.inner.set_len(new_len);
    }

    #[inline]
    unsafe fn bytes_mut(&mut self) -> &mut [u8] {
        let len = self.len();

        // This will never panic as `len` can never become invalid
        &mut self.inner.as_raw()[len..]
    }

    #[inline]
    fn put_slice(&mut self, src: &[u8]) {
        assert!(self.remaining_mut() >= src.len());

        let len = src.len();

        unsafe {
            self.bytes_mut()[..len].copy_from_slice(src);
            self.advance_mut(len);
        }
    }

    #[inline]
    fn put_u8(&mut self, n: u8) {
        self.inner.put_u8(n);
    }

    #[inline]
    fn put_i8(&mut self, n: i8) {
        self.put_u8(n as u8);
    }
}

impl IntoBuf for BytesMut {
    type Buf = Cursor<Self>;

    fn into_buf(self) -> Self::Buf {
        Cursor::new(self)
    }
}

impl<'a> IntoBuf for &'a BytesMut {
    type Buf = Cursor<&'a BytesMut>;

    fn into_buf(self) -> Self::Buf {
        Cursor::new(self)
    }
}

impl AsRef<[u8]> for BytesMut {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        self.inner.as_ref()
    }
}

impl ops::Deref for BytesMut {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &[u8] {
        self.as_ref()
    }
}

impl AsMut<[u8]> for BytesMut {
    fn as_mut(&mut self) -> &mut [u8] {
        self.inner.as_mut()
    }
}

impl ops::DerefMut for BytesMut {
    #[inline]
    fn deref_mut(&mut self) -> &mut [u8] {
        self.inner.as_mut()
    }
}

impl From<Vec<u8>> for BytesMut {
    fn from(src: Vec<u8>) -> BytesMut {
        BytesMut {
            inner: Inner::from_vec(src),
        }
    }
}

impl From<String> for BytesMut {
    fn from(src: String) -> BytesMut {
        BytesMut::from(src.into_bytes())
    }
}

impl<'a> From<&'a [u8]> for BytesMut {
    fn from(src: &'a [u8]) -> BytesMut {
        let len = src.len();

        if len == 0 {
            BytesMut::new()
        } else if len <= INLINE_CAP {
            unsafe {
                let mut inner: Inner = mem::uninitialized();

                // Set inline mask
                inner.arc = AtomicPtr::new(KIND_INLINE as *mut Shared);
                inner.set_inline_len(len);
                inner.as_raw()[0..len].copy_from_slice(src);

                BytesMut {
                    inner: inner,
                }
            }
        } else {
            BytesMut::from(src.to_vec())
        }
    }
}

impl<'a> From<&'a str> for BytesMut {
    fn from(src: &'a str) -> BytesMut {
        BytesMut::from(src.as_bytes())
    }
}

impl From<Bytes> for BytesMut {
    fn from(src: Bytes) -> BytesMut {
        src.try_mut()
            .unwrap_or_else(|src| BytesMut::from(&src[..]))
    }
}

impl PartialEq for BytesMut {
    fn eq(&self, other: &BytesMut) -> bool {
        self.inner.as_ref() == other.inner.as_ref()
    }
}

impl PartialOrd for BytesMut {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        self.inner.as_ref().partial_cmp(other.inner.as_ref())
    }
}

impl Ord for BytesMut {
    fn cmp(&self, other: &BytesMut) -> cmp::Ordering {
        self.inner.as_ref().cmp(other.inner.as_ref())
    }
}

impl Eq for BytesMut {
}

impl Default for BytesMut {
    #[inline]
    fn default() -> BytesMut {
        BytesMut::new()
    }
}

impl fmt::Debug for BytesMut {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(&debug::BsDebug(&self.inner.as_ref()), fmt)
    }
}

impl hash::Hash for BytesMut {
    fn hash<H>(&self, state: &mut H) where H: hash::Hasher {
        let s: &[u8] = self.as_ref();
        s.hash(state);
    }
}

impl Borrow<[u8]> for BytesMut {
    fn borrow(&self) -> &[u8] {
        self.as_ref()
    }
}

impl BorrowMut<[u8]> for BytesMut {
    fn borrow_mut(&mut self) -> &mut [u8] {
        self.as_mut()
    }
}

impl fmt::Write for BytesMut {
    #[inline]
    fn write_str(&mut self, s: &str) -> fmt::Result {
        if self.remaining_mut() >= s.len() {
            self.put_slice(s.as_bytes());
            Ok(())
        } else {
            Err(fmt::Error)
        }
    }

    #[inline]
    fn write_fmt(&mut self, args: fmt::Arguments) -> fmt::Result {
        fmt::write(self, args)
    }
}

impl Clone for BytesMut {
    fn clone(&self) -> BytesMut {
        BytesMut::from(&self[..])
    }
}

impl IntoIterator for BytesMut {
    type Item = u8;
    type IntoIter = Iter<Cursor<BytesMut>>;

    fn into_iter(self) -> Self::IntoIter {
        self.into_buf().iter()
    }
}

impl<'a> IntoIterator for &'a BytesMut {
    type Item = u8;
    type IntoIter = Iter<Cursor<&'a BytesMut>>;

    fn into_iter(self) -> Self::IntoIter {
        self.into_buf().iter()
    }
}

impl Extend<u8> for BytesMut {
    fn extend<T>(&mut self, iter: T) where T: IntoIterator<Item = u8> {
        let iter = iter.into_iter();

        let (lower, _) = iter.size_hint();
        self.reserve(lower);

        for b in iter {
            unsafe {
                self.bytes_mut()[0] = b;
                self.advance_mut(1);
            }
        }
    }
}

impl<'a> Extend<&'a u8> for BytesMut {
    fn extend<T>(&mut self, iter: T) where T: IntoIterator<Item = &'a u8> {
        self.extend(iter.into_iter().map(|b| *b))
    }
}

/*
 *
 * ===== Inner =====
 *
 */

impl Inner {
    #[inline]
    fn from_static(bytes: &'static [u8]) -> Inner {
        let ptr = bytes.as_ptr() as *mut u8;

        Inner {
            // `arc` won't ever store a pointer. Instead, use it to
            // track the fact that the `Bytes` handle is backed by a
            // static buffer.
            arc: AtomicPtr::new(KIND_STATIC as *mut Shared),
            ptr: ptr,
            len: bytes.len(),
            cap: bytes.len(),
        }
    }

    #[inline]
    fn from_vec(mut src: Vec<u8>) -> Inner {
        let len = src.len();
        let cap = src.capacity();
        let ptr = src.as_mut_ptr();

        mem::forget(src);

        let original_capacity_repr = original_capacity_to_repr(cap);
        let arc = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;

        Inner {
            arc: AtomicPtr::new(arc as *mut Shared),
            ptr: ptr,
            len: len,
            cap: cap,
        }
    }

    #[inline]
    fn with_capacity(capacity: usize) -> Inner {
        if capacity <= INLINE_CAP {
            unsafe {
                // Using uninitialized memory is ~30% faster
                let mut inner: Inner = mem::uninitialized();
                inner.arc = AtomicPtr::new(KIND_INLINE as *mut Shared);
                inner
            }
        } else {
            Inner::from_vec(Vec::with_capacity(capacity))
        }
    }

    /// Return a slice for the handle's view into the shared buffer
    #[inline]
    fn as_ref(&self) -> &[u8] {
        unsafe {
            if self.is_inline() {
                slice::from_raw_parts(self.inline_ptr(), self.inline_len())
            } else {
                slice::from_raw_parts(self.ptr, self.len)
            }
        }
    }

    /// Return a mutable slice for the handle's view into the shared buffer
    #[inline]
    fn as_mut(&mut self) -> &mut [u8] {
        debug_assert!(!self.is_static());

        unsafe {
            if self.is_inline() {
                slice::from_raw_parts_mut(self.inline_ptr(), self.inline_len())
            } else {
                slice::from_raw_parts_mut(self.ptr, self.len)
            }
        }
    }

    /// Return a mutable slice for the handle's view into the shared buffer
    /// including potentially uninitialized bytes.
    #[inline]
    unsafe fn as_raw(&mut self) -> &mut [u8] {
        debug_assert!(!self.is_static());

        if self.is_inline() {
            slice::from_raw_parts_mut(self.inline_ptr(), INLINE_CAP)
        } else {
            slice::from_raw_parts_mut(self.ptr, self.cap)
        }
    }

    /// Insert a byte into the next slot and advance the len by 1.
    #[inline]
    fn put_u8(&mut self, n: u8) {
        if self.is_inline() {
            let len = self.inline_len();
            assert!(len < INLINE_CAP);
            unsafe {
                *self.inline_ptr().offset(len as isize) = n;
            }
            self.set_inline_len(len + 1);
        } else {
            assert!(self.len < self.cap);
            unsafe {
                *self.ptr.offset(self.len as isize) = n;
            }
            self.len += 1;
        }
    }

    #[inline]
    fn len(&self) -> usize {
        if self.is_inline() {
            self.inline_len()
        } else {
            self.len
        }
    }

    /// Pointer to the start of the inline buffer
    #[inline]
    unsafe fn inline_ptr(&self) -> *mut u8 {
        (self as *const Inner as *mut Inner as *mut u8)
            .offset(INLINE_DATA_OFFSET)
    }

    #[inline]
    fn inline_len(&self) -> usize {
        let p: &usize = unsafe { mem::transmute(&self.arc) };
        (p & INLINE_LEN_MASK) >> INLINE_LEN_OFFSET
    }

    /// Set the length of the inline buffer. This is done by writing to the
    /// least significant byte of the `arc` field.
    #[inline]
    fn set_inline_len(&mut self, len: usize) {
        debug_assert!(len <= INLINE_CAP);
        let p = self.arc.get_mut();
        *p = ((*p as usize & !INLINE_LEN_MASK) | (len << INLINE_LEN_OFFSET)) as _;
    }

    /// slice.
    #[inline]
    unsafe fn set_len(&mut self, len: usize) {
        if self.is_inline() {
            assert!(len <= INLINE_CAP);
            self.set_inline_len(len);
        } else {
            assert!(len <= self.cap);
            self.len = len;
        }
    }

    #[inline]
    fn is_empty(&self) -> bool {
        self.len() == 0
    }

    #[inline]
    fn capacity(&self) -> usize {
        if self.is_inline() {
            INLINE_CAP
        } else {
            self.cap
        }
    }

    fn split_off(&mut self, at: usize) -> Inner {
        let mut other = unsafe { self.shallow_clone(true) };

        unsafe {
            other.set_start(at);
            self.set_end(at);
        }

        return other
    }

    fn split_to(&mut self, at: usize) -> Inner {
        let mut other = unsafe { self.shallow_clone(true) };

        unsafe {
            other.set_end(at);
            self.set_start(at);
        }

        return other
    }

    fn truncate(&mut self, len: usize) {
        if len <= self.len() {
            unsafe { self.set_len(len); }
        }
    }

    fn resize(&mut self, new_len: usize, value: u8) {
        let len = self.len();
        if new_len > len {
            let additional = new_len - len;
            self.reserve(additional);
            unsafe {
                let dst = self.as_raw()[len..].as_mut_ptr();
                ptr::write_bytes(dst, value, additional);
                self.set_len(new_len);
            }
        } else {
            self.truncate(new_len);
        }
    }

    unsafe fn set_start(&mut self, start: usize) {
        // Setting the start to 0 is a no-op, so return early if this is the
        // case.
        if start == 0 {
            return;
        }

        let kind = self.kind();

        // Always check `inline` first, because if the handle is using inline
        // data storage, all of the `Inner` struct fields will be gibberish.
        if kind == KIND_INLINE {
            assert!(start <= INLINE_CAP);

            let len = self.inline_len();

            if len <= start {
                self.set_inline_len(0);
            } else {
                // `set_start` is essentially shifting data off the front of the
                // view. Inlined buffers only track the length of the slice.
                // So, to update the start, the data at the new starting point
                // is copied to the beginning of the buffer.
                let new_len = len - start;